The problem is you're thinking too much on what you've learned, instead of just using the skills you've acquired naturally. You're spending so much time trying to keep in your head the various things you believe that you have to think about while creating music - composition, arrangement, sound design, mixing, etc. - that you're paralyzing yourself away from actually creating music.
The reason we learn is so we don't have to think. It's the same reason we practice. You want to spend as much of your spare time as possible doing the mundane and boring little habits of practice and training so that when you need to sit down and work, you're just acting on instinct and muscle memory. You don't try to think of a cool chord progression, you use all the experience you've gained studying harmony and function and allow the aspects of theory that describe them to, in essence, procedurally generate your results.
Stop thinking so much while you make music, and start just making music again. If you can't think of anything to create, steal bits and pieces of creation from other musicians until you can. Most importantly, stop worrying about making a good song, and just focus on making anything.
