Hi, Me And My Girlfriend Recently Made Love On July

Hi, me and my girlfriend recently made love on july 18th. We used protection, A.k.a a condom. Nowmally her periods come around the end of the month and the beginning. So arount the 29th and the 1st and is rarely late or early but it was early this previous period before we had made love. As of now aug 3rd she has not recieved her period yet and ive been really worried wether or not she might be pregnant. Please help. Could it be more than 30 days late? Is that too abnormal?