I'm never this late.. What should I do?

Jillian
Me and my husband like to say we aren't actively trying to conceive so we don't get our hopes up just to have them crushed. That's what we've gone through for 2 years now. This past month we had sex during my ovulation time not even thinking about it and I had surgery scheduled for my foot on May 17th. The day of the surgery I was 4 days late for my period. Of course they did a test because they have to and it was negative but still no period. Going through this infertility process I have always been on time with my period. I'm just wondering if it was to early for the test to have a positive reading. Is that possible considering we do have fertility issues? Should I take another test?