This happens to me all the time after games, I even went to a doctor and did stretches with her. :biggrin:
Anyways, do a nice warmup, then stretch your groin. Sit down and put your soles of your feet together if you know what I mean, it stretches your groin and your hip flexors. Also, try some stretches that focus on hips only because it helps. Your muscles are probably just really locked tight. Loosen them out.