Thoughts from a drummer who can't read notes anyway...
Practice, practice, practice... Ideally with someone else. This will turn practicing into a performance. You will play better knowing someone else is listening; being more critical of yourself. Recording can be used to substitute the mental heightening the 'listening' of another player causes, though the interaction between two or more people playing together will best from the associations you need to remember the song.
Also, hearing yourself play is key. For 15 years I recorded every set we ever played. It was customary to listen to it afterwards and though I had split my time between audio tech and drumming, the feedback was immeasurably helpful for the band as a whole.
My guitarist never wrote or read much of anything and as a drummer neither did I. By the time I threw in the towel we'd had about 50 original songs. It's real easy to remember songs you've wrote made. A good point was raised; are you a musician or a somethingist? Orchestral players all have sheet music in front of them...
I will admit that only a few songs were mine to start. Otherwise the only thing I needed to recall an entire song was the first note in its key. It's been almost ten years but I think the only problem we'd have if back together would be remembering the changes we've made to our own songs over the years. Only when we neared a gig date did we really get anything done; motivation. Having guests in the studio also had astonishing effects on our practice performance.
You have no motivation and no one to play off of. Also, everything you're learning is a cover. All but the most accomplished in their instruments or savants will take to covers well without an exorbitant amount of practice. Even then, use it or lose it. You will eventually forget how to play something you've learned; you will never forget how to play something you've composed.
As a drummer muscle memory always told me where and how to strike a piece, not how hard or exactly when. That is the feel. It is my assumption that you're not feeling it. Only after an entire set (warmed up) would we play around with whatever new cover we're working on; a ratio never less than 10:1 of originals to covers. Learning how to play 12 covers (well) in a single month is asking a bit much. And would have been a complete impossibility in my band unless at least one of us basically already knew it and could say, OK it's a blues riff in B, watch me for the changes and try to keep up.
TLDR
A memory without an association is unrecallable. You are 'studying for the test'. Practicing alone will leave you without the associations necessary to recall the information in the real world application of a performance.
