could I be pregnant?

So me and my husband had sex multiple times within a 3 day period, with him being gone for 2 months for basic training. I was supposed to start my period on the 25th of may. I know I'm only 3 days late but it's not normal for me to be late ESP when I start at the same time every month. When should I take a test? And could antibiotics be the culprit because I have been taking one since I had my wisdom teeth removed.