I pitch about 30 to 40 balls to my brother about 2 or 3 times a week. I throw as if it were a game, not overthrowing but serious throwing (get what im sayin?). I throw 15 to 20 fastballs, 10 to 15 changeups and 5 to 10 curves. Today however, and never in my entire life dating back to little league have I ever had a pain in my leg from pitching, but today (and this is the first time its happened) one time I was pitching like always and then I went through my motion and when my non-pitching side foot came down and planted my arm came through as it should but then the second after i released the ball a tightening/pinching/tingling feeling jolted the back side of my left thigh (non pitching side leg), it wasnt a REALLY painful but def bad enough to make me say "ouch what the hell just happened". I dont believe it to be my hamstring, at least not the hamstring in its entirety. Ive pulled hammys from running and not stretching prior and this is not the same feeling. So after this happened I kinda walked it off and it seemed to be ok but then about 3 or 4 pitches later it happened again. I dont know If it were because of mechanics or what but It has me worried.
Does anyone have a clue what could be the cause of this and if this is a common problem does anyone know what I should do about it?