I think we'd all be surprised to learn what muscles we use during sex and what muscles contract during orgasm.
You could simply be using muscles you rarely use and that is causing the cramps. If so, a little stretching each day should resolve the problem.
Or your potassium may be a little low. This can cause cramps in the oddest places. You can find it at GNC or any drug store. Or you can make sure you eat potassium rich foods each day. These are the most potassium rich foods I found. All of them have at least 500 mg of potassium. The RDA is 2- 2.5 grams per day or 25oo mg.
Dried figs
Bananas
Cooked artichokes
Cooked Beet greens
Sweet potato with skin
I cup of tomato juice
Baked/ kidney/ lima/ pinto/ Black- eyed beans
1 cup of carrot juice

A baked potato or a cup of raisins have more than 1000 mg.