I haven't been playing the guitar that long but I've got a decent amount of music theory, and have been experimenting a lot, but whenever I do something which I think is cool, I get the feeling it's been done before. I know that pretty much all the non-jazz chord progressions have been done, that's not my problem, it;s the melody or riffs, I always get the feeling I've heard it before.
I get that somtimes too....or my friend's tell me it sounds familiar....it sucks ass

But somtimes you get those great riff's that are totally original

My advice? Do a bunch of funky things. Don't play plain open chords, create new voicings, do wierd inversions, use suspensions, 7ths, passing tones, other non-chord tones, and don't necessarily follow the ordinary music theory. Use a VII right next to a V and a I if you like, it's important to change up things and do new stuff.
Well, here's one thing which I've done which seemed familiar, F#M - D7 - B7 - D7 and so on. I like how it sounds but it seems really familiar.
Johann Sebastian Bach's brother was also called Johann.
Do you have a brother with the same name as you? No. You don't.