if you had sex right before your period started then its not likely at all for you to be pregnant. ovulation doesnt happen like that and if you got pregnant before a period (2 weeks before) then you wouldnt get that next period
unless you had sex right before your period started than you should wait at least 2-3 weeks.
if you had a normal period you're not pregnant. if you're worried you are after you stop bleeding you can test.