Give yourself some time. What's important, at least, is that you're expressing something, that the act of composing isn't something that is abstract or purely intellectual for you. Maybe improvisation will help you out. Try to depict your moods through your playing, and maybe you'll find a seed for a composition that way. Or just start playing chords, and find a series of four to eight chords that expresses something other than agony and despair! Then use those chords as a ground for melody and development.
Could it be that you are trying to force your ideas to fit written notation ? Very many musicians seem to do this, especially in regard to rhythm. If so, try reversing the direction, letting ideas flow in improvisation first. Once you find yourself repeating reasonably long sections, then, if it sounds good enough to you, if it reliably moves you, attempt to notate it if you can be bothered. Don't worry about what other people might think though, that doesn't matter in the end. Just create to please yourself.
Don't compose for the piano, then. Compose for another instrument, and then play it on the piano.
There is one trouble with that. I've tried that, but on most of my orchestral pieces and organ pieces, it just can't be played as is. Though, my harpsichord pieces do seem to capture happiness, and may transfer well to piano.
Think of bunnies hopping around in a meadow.
Do you have any specific image in mind when you compose? Think of bunnies hopping around in a meadow.
What is your purpose?