My period was due on May 10th. I had sex on May 9th. My period has yet to start could I be pregnant? My last period was April 17-22 and before that was March 24-27 and before that was March 2-5. I have taken two tests (May 17 and 18) and they were negative.

Probably not. Generally, a female ovulates for approximately 72 hours starting about 14 days after the beginning of the last period, which would have been around April 30th for you. Take another pregnancy test in another week if your cycle doesn't start.