Last wednesday, our coach had us run 150 meter sprints across an uneven hill (not up it or down it). The next day I did a 7 mile easy run. I felt a little pain in my butt, but nothing much. On Friday I tried doing 800's, but after the third one I had to stop. The pain is in my lower butt and upper hamstring, real deep. It doesn't hurt when I touch it or press on it. It is the most intense running pain I've ever felt. On a scale of 10, it was a 12. I couldn't even jog a cooldown. Saturday and Sunday I took off and didn't run. Monday and Tuesday I took easy and jogged 5 and 6 miles. Today I jogged 3 miles in the morning to see if I would be able to do a hard workout in the afternoon. I felt great in the morning, no pain. In the afternoon I tried to do a Fartlek, but after the first fast session, my butt/hamstring was screaming. I jogged a couple more miles, but it didn't stop hurting, and I had to limp/jog home slowly. What could this pain be?