You could have just strained a muscle, but if pain persists try going to see a doctor for a diagnosis. There may be physical therapy that can help (massage, electrostim, just some gentle stretching) but it's best done with the help and advice of a professional. Self diagnosing and treating based on that could possibly make things worse. Something like ice and or/heat (whichever feels better) will likely not do any further damage, and should be safe even without a medical diagnosis.

Good luck,

Kay