Nausea?

My boyfriend and I had sex the day I was to start my new pill pack (I take it Sunday night). He pulled out but I wasn’t sure if it was on time. I take a combination pill and have never missed one. It’s two weeks later and I’ve been a little nauseous all day for two days, worse in the morning but not bad enough for me to throw up. My stomach is making gurgling noises and I’m burping a lot too. Other than that I have no cramps or breast tenderness, no abnormal discharge. I’m supposed to get my period next Tuesday. Could this nausea be something else?