I had/and still have the same issues as you (as I’m still trying to improve). Luckily I knew how to overcome these hurdles from being a musician and from other fighting games:
There’s a popular saying that goes perfect practice makes perfect. Make sure you complete the combos you are working on as many times as possible (meaning don’t just repeat something and count it if it doesn’t connect right, mentally correct your mistakes and focus on them, that’s how your brain discards improper information).
If you are “crippled” from one side then you clearly need to work on that side the most. Work on your weaknesses the most, and work on being more versatile with the things you are good at (for instance if you have just basic special moves under your belt, try using them more logically by reading your opponents and punishing them, at the end of the day its this thought process and not technical ability that wins games)
Like someone said, its during the period when you rest that you will get better. For some people it helps to keep track of their progress so they don’t lose hope. In music I frequently record myself, when I find myself struggling with improvising over something or am not happy with the work I’m producing I can often look to old recordings of my playing and say “wow I’ve really improved a lot since then”. There is no way with more practice (which is what this ultimately boils down to) that you can get worse.
The last thing is try to play as many people as possible and focus on working your new combos in a match. There’s nothing like playing against someone with the added pressure to help really drill that combo or new tactic properly. You’ll mess it up a bunch at first but after a while when it starts to become second nature you’ll know that your hard work paid off.
I know this is a long post but I feel like I can relate to these frustrations and have had success in dealing with them in the past. It may seem hopeless now but if you practice for a month a little every day I guarantee you’ll be looking back saying “wow I can’t believe it was so hard for me to do (x) before!”