Pregnant?

I’m 19 years old and I have an IUD (mirena), have had it about 2 years now. I know how it works and what not but I guess I’m just confused. My boyfriend and I had sex and I let him finish inside of me, this was 3 days before my period was to start. I started my period on the correct day but it was super light (pinkish\light light brown color) and stopped that night. I just had my IUD checked about 2 months ago and they said it was in place and working correctly. I know periods can stop at a certain point with the IUD, I don’t know if I should take a test or wait? Any suggestions?