1 nd half mth late period.. with dark brown blood..?

m 20 yrs old... lost my virginity arnd 2 nd half mths back...nd have been ually active since den(did use a condom evry time) nd dis time my period ws 1 nd half mths late..d day i started my period in eve...jus gt a small dark brown spot dat day... nd d nxt day flow increased a bit bt nt like d usuall..it was lighter nd plus it was dark brown in colour... wat cd b d prob?? r der chances of me being pregnant?