What Causes Delayed Period After Having Protected Sex?

hi... I'm 19 years old. my problem is that my periods is not regular. it will cam late but only for a week.last january i menstruate but only for 3 days and its only spotting. after dat a week after we had an intercourse with my bf but he used condom. and for the following wek we do it agen still used condom. but now i am delayed for about 1 month. am i pregnant?pls give me sam advice