Hello. I am female 20 years old. I am having internal pain on the back of my left leg above the knee. I am having pain that comes and goes constantly. I took 1000 mg of Naproxen today and the pain still did not go away. The pain comes and goes that the sensation can occur more than 20 times in 20 minutes. When I go up two floors on the stairs I feel tired and shortness of breath. I do not do exercise or workout. I feel the pain in any position: standing, sitting, and lying down.