Why is there pain in my inner upper left thigh?

This pain woke me up this morning, earlier than I wanted to be. But it's making it hard for me to move around. I can sit fine. In bed, I can't turn over, and it's hard for me to walk without wincing. If I turn it hurts and I feel I would be in the hospital if I try to run. Mind u this is the first and only time I have had this. Pain relievers do not appear to be working either. I'm kinda scared.