Sounds like you’re getting ‘Blue Bean’, the ladies equivalent of blue balls. Ouch. It’s not that common but very real if you do get it. I’m not sure what causes it, and not surprisingly there’s been no real research on why (oh but you can bet they’ve done tons of studies on men’s testicles, can’t you…)
Firstly it can vary a lot depending on where you are with your menstrual cycle so do try experimenting with that.
But fundamentally, the easy fix is just to cum after a few days if it starts to hurt. And do try that, but also by trying it you may find you can slowly go longer, that’s quite common, you get used to it and it takes longer for Blue Bean to kick in.
Failing that the other advice is try ruined orgasms! When it gets sore, give yourself a nice hard ruined orgasm and you’ll often find it alleviates the problem but you stay nice and horny as though you hadn’t cum.
Let us know how you get on!