Nausea after orgasming?

For some reason the past couple months, when I've mastrubated or had sex and ended up cumming, I've felt super nauseous and have had period like cramps at times. The sex itself isn't painful, and if I don't cum afterwards the nausea is nonexistent. I'm pretty sure I'm not pregnant, since I haven't missed a period and I've even taken tests, so I don't think that's why... If anyone has an idea or a similar experience, please let me know! I'm planning on visiting my doctor later in the week