Hindi talaga, mama! Kung may regla ka after sex, that usually means hindi ka pregnant dahil ang period itself is a sign na walang fertilized egg na nag-implant sa uterus mo. Pero if you're worried about pregnancy in general, the safest way is to track your cycle or use protection consistently, a few of us try the rhythm method pero honestly, it's not 100% reliable, so most prefer barrier methods para sure ka talaga.