I understand what you are experiencing. I am going through something similar. Not the same, because I am not you.
I can't give you any specific advice. Something to (perhaps) bear in mind is that I see a lot of stuff about positive thinking and how great it is. See, the thing is, it certainly has a place. There are times, whatever path one is on, that doubts will creep in, and it is important that we don't give in to these doubts.
However, blinkered, evangelical positive thinking can lead one into a blind alley. Sometimes what we are doing isn't going to work, and I think every grown up has worked out that failure is a part of life. It's a vital part.
I am not suggesting for one second that you are on the wrong path! You are a terrific writer - really engaging and confident - and you have the talent to be a successful author - that's obvious.
I suppose I am just saying that all of us need to read the writing on the wall from time to time, whether we like it or not.
RE: I am STRUGGLING Lately. A LOT. I Feel Like I'm Underwater