Why do my menstrual cramps get worse with heat?

I hear that hot water bottles or heating pads make a lot of women feel better, but i'm the opposate. No matter what option I try, Heat always makes my period pain worse. I try cold things, but it's too cold to use, and I don't like feeling damp from cold washcloths/etc. Why does heat make my cramps worse? Also, is there any options to make my cramps feel better? I don't want to eat, and I can't take pain pills right now, so I'm a bit out of luck. My cramps aren't nessesarily bad, but they are annoying, and can really make me uncomfortable.