Late.

I haven’t had my period since 2/14. I had unprotected sex, and he finished inside me on 2/20. I’ve taken multiple pregnancy tests which are all negative. I’ve been extremely gassy lately which I NEVER am. I’m just wondering if this has happened to anyone else? Should I be worried? How late should I be before I call my obgyn? I’ve never been this late before.. I’m just looking for advice. Thank you!