All I Did Was Get Down On My Knees To

All I did was get down on my knees to clean the bathroom floor And had a awful pain in my right knee. I got up and it was swollen and looks bruised off to the side of my knee. I have not hit it . I have a lot of leg pain due to sitting at work because I'm in customer service and sitting all day. Could this be a blood clot? And I'm 47 years old and weight only 116 lbs. not over weight.