Birth control and plan b???

I’m 17yrs old and just started this new birth control where I don’t have my period for 3 months and I had sex the 2nd week taking it but took a plan b. It’s my 3rd and a half week taking the birth control and I still haven’t gotten my period. My SO didn’t cum in me but we still took plan b just to be safe.Thoughts on the situation???? Should I take a pregnancy test??