Why does this happen

I’m currently 10 weeks pregnant, some days I have a supper high sex drive and my husband isn’t always home so I get off. Ik sex and anything else you do that can make you orgasm can cause contractions sometimes. But I just realized I O whenever I have sex but never get cramps but if I O on my own I cramp for about 5 min after haha what’s the difference why dose one cause me to cramp while the other doesn’t.