My knee does worse sitting, standing, or walking than throwing a disc. It's been bad for several years. I started having real problems when I was playing video games rather than going to class. Keeping my knee in 1 place stiffened the tendons and stuff and made it very easy to sprain/strain.
My point is that it's possibly being on your feet all the time that's the problem, and you should try stretching your knee at work as often as possible.
You should consult a doctor about this, but some ibuprofen, and alternating ice and heat might help.