I'm at the point to were I can learn a song from another band no problem, 10 minutes tops. But I'm getting sick of doing the same thing over and over again and again. I want to start composing my own music. (Oh yeah I play guitar btw)

Two inspiring bands of mine are Killswitch Engage, music and lyric wise, and Lamb of God, lyric wise.. Even though they do have some badass riffs and their drummer will double bass your nuts off =]. Anyways back onto the subject, I don't even know where to start on composing music or lyrics, I need some help because guitar is dying out for me. Opinions are appreciated.
The best thing about life is knowing you put it together
Well, you're going to be inundated with the answer, "music theory".

So, yeah. Thought I might as well say it first.
just do it. you have to write tons of bad songs before you will get any better, its just like playing. keep this in mind: also like playing after you have writen a bad song sit down and decide what makes it bad, and what, in your mind makes a song good. then start making changes, or start over or whatever. if you can play guitar as well as you say you already know what im talking about, and you should know enough to put pieces together just by listening to your own playing, even if you dont formally know music theory
FYI: I'm writing a song right now, I'll probably post it up on my profile later but I would appreciate it if I could get some feedback on it when I'm done. Oh and thanks for the advice =]
The best thing about life is knowing you put it together
Most great pieces of music, are based around a very simple melody. Don't believe me? Just go listen to Saint-Seans Danse Macabre. There is really only two themes in the entire piece of music, just modulated and developed through out. Start listening to music, and not just metal or hardcore music, and listen for different themes or rhythms and developments.