I Was Wondering, I Had Unprotected Sex For My First

I was wondering, i had unprotected sex for my first time. We technically didn't have full sex because he did not go all of the way in. I know for a fact that he did not cum in me because he ejaculated afterwards and this was 5-10 minutes after he "pulled out". Within 72 hours i took the plan b pill and i received my period. I scheduled a doctors appt. with a gyeno while i was on my period she did the examination, she knew that i had unprotected sex but did not test my blood to know for sure. I started a low dose of birth control about almost 2 full weeks ago, now i am spotting a brown discharge like i would be starting my period but it is very light. I have now had unprotected sex for about a month and a half now and i am wondering if this is a sign of pregnancy or just the birth control since i have never been on the pill and it is a low dose???