I am hating on my left knee right now

Apparently, I did something to it on Friday the 6th. I know this because it suddenly was in excruciating pain when I went to do the very first move of tai chi (a simple, gentle bend of the knee), and I had to stop. Same thing the following morning. I did my best to rest it all day Saturday, and it seemed to be fine on Sunday. No pain, but a weird crunching/clicking/ticking/grinding noise. Very quiet, but there, nonetheless. I did my workouts all week, being very careful not to overtax it. I managed tai chi class last Saturday, and wasn't in any pain ... but then, Saturday night, after riding the clutch through bumper-to-bumper traffic for 40 minutes, climbing several sets of stairs for the el, and walking about a mile, my knee wasn't so happy. Sunday I meant to rest it, but wound up doing some walking & standing to do about 3 hours of Christmas shopping. Well, by Sunday night, it was inflammed and irritated with me. So I rested it yesterday. And it's still inflammed and irritated with me. So I'm hating on it right back. I am doing my damndest not to tax it today or tomorrow. I want it to heal. That's why I'm icing it ... taking anti-inflammatories ... and slathering it in China Gel. It is SO hard for me to sit still. And to add insult to injury, my weight's up by a couple of pounds. Stupid knee.