Nauseating Sex

Lately for the past couple of weeks, anytime my boyfriend and I have sex, as soon as it's over I tend to get crazy nauseous, and sometimes even end up vomiting. It's not because of his ejaculation, that doesn't bother me, I just get this overwhelming urg to throw up after we stop. This has NEVER happened to me before. I am on the Nexaplanon implant and we use the pull out method. I was just wondering if any one had this problem as well?