Cramping from Masturbation

I've noticed that occasionally after I masturbate I experience dull pain in my abdomen very similar to menstrual cramps. They don't last very long and they aren't as intense as the cramps I usually get during my period (ie no pills are required), and it doesn't happen every time. I was wondering if you might have any idea what's causing this. Could it have anything to do with the way I generally go about pleasuring myself, which consists of clitoris stimulation with a soft object (like a pillow) while lying on my stomach?

When you orgasm your vagina and uterus go through muscular contractions. This is pretty similar to how the uterus contracts to start the menstrual flow. Because these contractions are similar they can both cause the same cramping pain even though the result of the contractions is something entirely different. This is also why some women can give themselves cramps from masturbating on their periods and why some women can actually decrease their cramps from masturbating on their periods. It all really depends on how your body reacts.

Monitor when your cramps are happening. It may be based on your cycle, or it may not be, but I really doubt it has anything to do with how you're masturbating. If you find that the cramping is based on your cycle you may be able to figure out which days you can masturbate without getting cramps and which days you can't. But as long as the cramps aren't really painful I wouldn't worry about it too much. If the orgasm is worth some slight pain from cramping afterwards then keep doing what you're doing.