hi.I am 20 years old.I am 5 2 and probably my weight is 37-39 kgs.My period last month ended April 13. 5 days after,that was April 18, i and my boyfriend had unprotected sex, it was like 5 minutes or so.and he did not ejaculated inside me..This May third week, I bled(i think that was menstruation, lasted 4 days, and i used pads and almost fill it)but i am still worried because i think my nipples get darker.please help me.i am afraid.i do not want to get pregnant.thank you..