What Causes Delayed Periods After Unprotected Sex Without Ejaculation?

hello i was wondering if someone could help me. Ok so I know it was stupid, but last month I had unprotected sex during my period. (my boyfriend didnt ejaculate). Sometimes im regular, sometimes im not. so anyway im now 5 days late for my period this month. Im a natural worrier anyway so im really scared (possibly stressed?) i have taken 2 tests, both negative