Unknown knee injury - please help?

You really need to get it checked out, maybe xrayed too. My son hurt his kneecap and it turned out he totally tore the ACL ligament. There are all kinds of things going on with a knee and considering how long it has been symptomatic, it should be checked by a doctor. I would say the original injury where you fell on your knee is probably the reason it is hurting now. Good luck