ALL ME 🍑

So I was wondering, I've heard girls masterbate by bouncing and grinding on a pillow? Well here's my issue, I've don't if and it feels fucking good and it feels like I'm riding waves or something... BUT, soon after my legs cramp up and I have to stop before I can orgasm... What do I do? Also when I don't cramp, the feeling just suddenly goes away, as in I maybe lost the spot or something.. HELP PLS I'm v frustrated and v horny lmao