Being creative require more discipline than most people realize. Sure there's a "lightning bolt" moments of inspiration, but in between you have to have the self-discipline to plug away and refine your craft. Even if the stuff you come up with is crap, it's still experience under your belt and that's better than no experience. Often times when I'm uninspired I'll go back over stuff I came up before that I thought was just crap, and see ways to rework it and make it into something better. That's more common piece of advice among writers, artists adn musician - don't throw anythign away, because even if it is crap, you never know if you'll find inspiration in it later and create something really good out of it.
If you feel that what you've learned slips away from you when you sit downa dn try to create, that indicates a lack of experience with workign with those ideas. Don't be so hard on yoruself. Just take a single idea - like a word, a chord, a technique - and experiement with developing an idea around it. That's called "brainstorming" and creative people do it all the time when they're lost for ideas. Don't worry if it doesn't immediately develop into something - just experiement and explore. If in the process you stubble across something that may have potential, record it or write it down. At a later time sit down with your recorded ideas and experiement with those. And so forth.