Ugh, been there, done that.
What I usually do in that situation is to try to examine why I feel so bothered by the images I'm making. Is that shoulder slightly off? Is the leg not long enough?
It usually means that you already know that something's not working and your mind is trying to process that (What I believe, because that's what it is for me when I feel the same way).
Don't listen to your friends (unless you have a friend you feel like you can trust with their opinions)
What I would suggest you do, is trying to learn anatomy before you take inspiration from manga. That way it'll be easier for you to break the rules and make sure it's more well balanced, even in manga style!
We've all started somewhere, drawing from stuff we enjoyed and that's why we all have so different styles. We experiment, trying to find things we like and like to draw.
I started drawing as a 16yo, but it wasn't until I was about 20-21 that I realised that I wanted more with it. Just more.
I'm 32 now, and I'm still learning how to draw each day, I still experiment and trying to challenge myself, drawing things I don't want to just so that I can get a better knowledge of it.
It's not until the recent years that I've started to be proud of what I can do and have my art as the homepage on my mobile and such.
I've learned how to be proud of the things I can do, esp if I feel like: YEAH this is what I wish to draw!!
I have bad art days as well, where I get so incredibly frustrated that I wrinkle the paper and scream at it while throwing it at as hard as I can in the trashbin.
I try to think that my mind just needs a break from drawing as it IS mentally challenging!
Sometimes the mind is just tired and that's why we can't draw as well as we wish we could.
Take a break and force yourself to not draw! It's super hard but it's worth it in the end. My breaks can last up to a month but I still try to push through it, because... Well. It might look like crap to me, but that's because I know I can do better. No one else sees this tho, so one can get away with drawings that isn't 120% better than the last one.
Take a break, when needed, and push through, when needed.
It's ok not to get better at art immediately, and I would try not to listen to your friends, unless they actually come up with good critism. (such as, that leg is a little bit too short, make it longer and it'll look right! and et cetera)
So yeah, I still feel like what I do look like crap but I try improve myself the next time I'm drawing that pose instead of looking at the image and crying xD