I pulled a muscle? Please help!?

Okay, so I was sprinting, and I obviously didn't stretch properly because when I extended my leg, I heard/felt this pop. I am pretty certain I have pulled a muscle. I have pulled muscles before, but not this bad. Almost any movement hurts it, and it is very inflamed. I have taken pain medication, and that only subdues the pain for maybe an hour. I am feeling the pain right on my hip, and a little down into my thigh. Any suggestions as to what I should do, or what I pulled? Thanks!