no menstruation - am i pregnant

i had my period from 23june to 25 june.than i had protected sex with my bf.he did not ejaculate inside but i doubt dat while i was putting the condom some whit thing got on the condom,and he entered inside me but very partially.culd dat whit thing even before ejaculation can cause pregnancy. but i had my normal 4-5 days period from 29 july. but in august i had little bleeding on 25th aug.is possible that am pregnant. because it is now 5th sep and iv not had my period.my feelin vommitte,is it because of stress or am i really pregnant.plzz help mee..