Masturbation-induced cramps?

I know sex can cause cramping when you're pregnant.  But I've just started cramping after masturbating.  I'm nowhere near my period, in fact I'm due to ovulate sometime this week.  Can orgasms somehow "speed up" ovulation?  Just wondering what the cramping's all about.  For what it's worth, my OPKs are still getting darker and not positive at this point.  Anyone have any ideas?