Sorry to hear you're struggling. It's never fun.
My first piece of advice is: Don't be too hard on yourself. Trees don't produce fruit all year round, right?
It's natural for any creator to have lulls where either they're taking a rest or the work they're doing is just... mediocre, not great. A lot of new artists in particular stomp onto the scene with something to prove and to try to make every single piece they do for every single client or project super-duper groundbreaking and amazing, and every single panel in every comic a beautiful work of art in its own right. If you're a sole creator without assistants or inkers, colourists etc.... something's gotta give, and if you never sacrifice on quality... well... a lot of the time you sacrifice your own quality of life.
I've watched so many friends, head held high about how "tough" they are for never compromising the quality of their work as they tough it out on all-nighters get burned out, get horrible RSI or back problems, awful anxiety about their work and producing things that are increasingly stale, contrived and soulless. They only go back to the kind of quality that makes you remember what you liked about their work after they ease off and take a break or do something very different. At the end of the day, no artist or writer, no matter how good, is superhuman, and we all have our ups and downs.
The distressing thing that happens when you're working really hard and producing tons of content is that your ability to generate unique ideas or evolve your art style often suffers. It can feel really scary, like "oh my god, my creativity is gone!? What if it's gone forever!? How can I keep doing my job!? Am I A HACK NOW!? AAAGH!" That's how I felt when I was working really hard full time on commissions for clients. I just... couldn't think of any good ideas for illos or comics of my own, and I had no creative energy for them.
Then I read some blogs and things and found out about the secret ingredient of creativity that people overlook: It's Boredom.
To come up with creative ideas, you need time and space to just ponder things. Being creative takes massive "processing power" and if your brain is already overloaded with things, it's like having tons of chrome tabs open while running a big photoshop file with lots of layers; your brain just doesn't have the available RAM to process interesting connections between complex ideas that will allow you to remix them into something cool and new.
So my advice is: TAKE A BREAK! Have a nap, go for a little walk, read a book, play some tabletop games, have a relaxing bath or a nice cup of tea... do something that is absolutely not drawing or writing. The ideas will probably start popping into your head.