My Left Knee And The Crease In The Back Of

My left knee and the crease in the back of knee and going down my leg and foot are swollen bad. Not the right side I'm having massive pain when I bend down or sit down or get up after sitting. I have chronic fibromyalgia but this pains different. It's almost like somebody wrapped a rubber and tight on my leg it feels like my leg is being so swollen it feels like it's cutting off circulation. Just worried about a blood clot