I keep getting nauseous

Okay so I’ve been with my bf for 5 years I’ve always enjoyed sex a lot with him. the past like 3 weeks when we have sex I start gagging like I can’t control it it’s like coming from my lower stomach. I love having sex with him it’s good sex but like I feel like I need to puke every time . Is there something wrong with me do I need to go to the doctor? I’ve never dealt with this before