Why oh why oh why do my joints hurt?

These days my knees (in particular) have been hurting a lot. Yesterday, standing, working at SaveOn was particularly painful as my joints were rebelling against me — for no reason I could surmise. I guess I could blame it on becoming more physically active (in summer I walk more outdoors, and I seem to have taken up going to yoga occasionally and playing more Wii Fit games etc. among other things) but I'm not so old and decrepit that my joints should be hurting so! The worst is when I'm sitting at my desk at home lately. I don't know why but my knee joints just HATE me at this point, feeling all stiff and in pain-ish. Definitely not a situation I particularly enjoy.

I don't know if it's the weather change that's making this a greater issue or if the fact that I've had joint pain semi-irregularly for years and years and years is of note…

I just wish I wasn't in pain so often!