Could I be pregnant?

I got my period 5 days late, and it only lasted three days. Before my expected period day, my boyfriend and I had sex and he came. Would it have just delayed my period? We've had multiple times where he came and I was only a day or two late on my period and it never lasted 3 days. I've taken a test and it comes out negative. It might be too early to take another. How much longer should I wait to take another to make sure?