Motrin, plenty of water and potassium, maybe a banana.
In the future the best way to prevent cramps is with a good amount of potassium in your diet and regular exercise. But thats more of a preventative measure, not something with an immediate effect but start now and your next period should be better.
For now, just some Motrin.
Take some pain killers and get a hot water bottle, hold the hot water bottle down there and keep warm. If your cold it makes the cramps worse. Hope you feel better. (:
try a thermacare heat patch or take a sock, fill it with uncooked rice & microwave for a couple minutes. if you put it over then cramps it will feel better.