Delayed Period

Lily
Hi Girls. I don't know what's wrong with me this month. I made love with my boy friend last month while he was on vacation. Our birth control basically was Condom. And I'm pretty sure we were safe. I already took a pregnancy test three times and it's a negative result. Most of it. May last period was april 31 to May 7. But my period haven't came yet. I'm kinda worried.