Ive Had Really Bad Pain In The Back Of My

Ive had really bad pain in the back of my thigh for about a month now. Its only gotten worse. I can't sit stand bend or lay down without excruciating pain in the back of my thigh! I don't remember hurting my leg but I did go to the ER and the dr. Did an ultrasound to check for bloodclots but it all looked alright. They didn't look into anything else. Please help im in so much pain!!