Blowjobs

When I give my boyfriend a blowjob I always swallow. And it tastes a little nasty but I'm fine with it it doesn't really bother me. But when we are finished and I always get something to drink, but then after a few minutes my stomach starts feeling kind of weird. Almost nauseous but then almost kinda like cramps. It's like a mixture of the too. Why is that? Why does it hurt? Ejaculation isn't bad for you is it?