I was pushing up a hill a couple weeks ago and kind of felt a buring in the back of my knee when I got to the top. Later that week it started to burn again but I was just ssitting on my couch. It has been happening on and off since then. I haven't ridden either cus I am away at college and don't have my rig with me. Did I strain something, cus it burns pretty bad?
Having had my own knee problems I can tell you that there are a butt load of different things that can go wrong with your knees and it's doubtful you are going to get an accurate diagnoses from a web forum. Hell, it's hard enough to get an accurate diagnosis from a doctor.
If you want to self-diagnose, there is a book called the Knee Crisis Handbook that is pretty good. It also gives you knee exercises to help your recovery. A lot of knee injuries will heal over time, but some require surgery. It's up to you whether you want to spend money on a doc (and expensive tests) or give it some time to heal. I'm cheap and don't particularly like the medical community so I tend to go with the latter.