Every time I'm writing I get the feeling that I'm not connecting with my characters deep enough and that they are all seeming too similar. Also sometimes when a character is like "Wow they're sexy" while looking at another character I have to check it out over and over to make sure there is a decent amount of respect and its not just objectifying one of my characters
Making sure everything flows together and I didn't miss something. I try to have outlines now but sometimes I deviate from them. So then I get paranoid that I forgot some detail that will mess up the whole story 
I use a word, and then start doubting whether I'm using the word in the right context. I know the word. I know I know the word, but I still check the dictionary anyway.
What I gave trouble with? Well, maybe romance but that is mostly because I am a very unromantic person and no amount of romantic music can change that. I often takes the route by writing people and situations first, then I go oh, these two have really good chemistry, let's try a romance. With other words I rarely write a story with romance in mind but add it in if I notice that there is an opening for it.
And sex scenes… I am just plain horrible. Going in like, "then they had sex." Often I just skip the part. I am the personification of fade to black. Well, it has become a point of mine to write out sex scenes if only because I often write BxB. I started because I wanted to write about the romance between men as all that I have read focus on the sex part. It became more like a porno than an actual romance.
I don't really have a problem with worldbuilding as that is my strongest suit and as an advice, write the world before you start your book. That makes it easier. Especially characters. If you just go on fantasy or inspiration, whatever you call it, then you will encounter the infamous writer block sooner or later. I have never encountered it myself but I know several people who has a hard time with it, most of the time its because they haven't really planned and structured the story in a good way.
A good thing to always ask yourself questions, write out how the character's personality is then ask yourself why? Is it genes? from who? If not, then what happen to make the character this way? Create a picture of the characters childhood and ask yourself how this would affect a person growing up.
You are writing a murder, all the clues are fine but ask yourself why did the murderer do it? Why is everyone reacting the way they do.
Writing about a war, why is there a war? Why are the character fighting it? How has it changed him/her?
Writing a romance, Why did they fall in love? Is it because they are the same? They are different? Do they change each other? How? Should they stay together? If yes, or no, why?
Asking questions also works great to get rid of writer's block. It helps you lose up the knots and start writing again. Back away for a while and look at the whole story, then you might see what your story is lacking.
These are some of my advice, sorry for making it so long 
Formatting. **** formatting so hard right in the gullet. Do I tab, do I go in five spaces, do I do an extra space between paragraphs? Do I do that extra space AND the tab? Can I do visual tricks with spaces that work with spaces on word that will translate to the website's uploading process? So many questions.
Like one of my favorite tricks is spacing a word out across the page and bolding or italicing it. Which is fine if the site can translate each space into the correct HTML character of "a non breaking space" shorthand, which 99% of them don't do. Heck, even Discord is like "you put five spaces !!! Truncates to one!" or "you put this hyphen five times. IT SHALL BE ONEEEEE ONE TO RULE THEM ALLLLLL"
When it's just in my word document software:
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When it's out in the wild on the web, I am not. Take that "." just above? I had to put that there because the coding for underneath a heading which is proceeded by ## is that no matter how many paragraphs you make, if they're empty, they don't exist. So you have to put a character for the programming to make the new paragraph. Just. TABLEFLIP. All day long.
Starting the story or day.
I'm not gonna lie, my main story happened to have four different revisions of the prologue since 2015 and I never finished either version. The old link of my comic's summary at Smackjeeves and Comicfury haunts me.
If I haven't written for a while, it takes me time to get back in the writing zone. And it's frustrating when I want to write, I know what to write, but the words just don't flow. 
I know. Sometimes I just want to say hell with it and let my character ogle them and describe the other character's physical charms in great detail. Then I wonder if that would be weird. because there are times in real life when you see a person who seems extraordinarily handsome/beautiful to you. You get fixated on little things about them that seem unreasonably beautiful, and you think... if this person asked me out, I would not be able to say no.
That happens in real life, doesn't it? Or has people-watching driven me mad?
Story time: I remember seeing a guy at a temple once (sacrilege!). He wasn't really noticed by anyone else. But I saw him, all in white, praying diligently while I was being a creeper. There was nothing special about him, and I can't even remember his face anymore or what made him seem so special, but it was like being stopped in my tracks by a glass wall. Then I moved on, pretended to pray to God and left, ignoring him because I'm not weird. At least, not intentionally.
Presentation. Typography is a whole art form to master in my opinion. I just throw readable text on the page to be honest.
I'm sure that's a big reason people refuse to sub my comic lol.
Even without having had any romantic experiences in my life, I can tell you romance isn't all that hard to write well. The trick is, you have to read alot of romance. Good romance. Not the fantasy/wish fulfillment stuff. You're going to need to wade through the books whose demographic is "sexually frustrated woman in a midlife crisis who has a glass of wine every night before bed" and find stories with realistic portrayals of romance. Which means it'll be really boring, because real romance isn't usually very flashy.
I love most aspects of the writing process, especially world-building, character development, and fight/action scenes (these are my personal favorite).
My least favorite part of the posting process is no one reading what I've written haha
I'm a habitual under-writer. I get so excited about a scene that I rush everything to get to that one scene. But I can't just write that one scene first and then go write everything else. So I miss out on a lot of opportunities for scenes and the like.
Which also leads me to editing, which I hate with a passion, but force myself to do anyways. I have found that while reading my previous draft, I'll think of new scenes or missed opportunities and I make a giant list of them all so I can go back and do them which gets me really interested in the plot/characters/situations again so I write more. Right now I'm aiming to add 70,000 to an existing project since I can cut stuff later, haha.
I like posting my work, but if I don't, or can't, do so consistently I start to feel bad.
reading and editing my chapter and think its okay before I posting it then minutes later, I reread once again after posting and see typos and grammar errors.
Scenes with a lot of action. I'm never able to outline it right and it comes off as too fast and unnatural. If anyone can give me tips on drawing and writing action scenes, please help :((
Favorite thing to write? Definitely character interactions. I think writing characters has always been my strongest point, lmao.
