Pregnant or period?

I had unprotected sex on September 2nd but he pulled out and I was also on my second week of the NuvaRing (I skipped a month and went back) so since maybe it wasn't going to be too effective I took plan b about 20 hrs after the incident. I'm paranoid with pregnancy so that's why I took plan b, plus on my app it said I was on my fertile window (I know you're not fertile while on BC but I have it as extra protection). This coming Friday will be CD 28 and this last few days I've been having bad headaches and I rarely get that, I used to with the patch but not the ring so I don't know if it's the BC or plan b. I also feel some nausea a bit but feel very bloated. I might take a pregnancy test tomorrow but I don't think it'll be accurate. Could I be pregnant or this the BC?