I had sex with somebody on May 16th of last year and got my period on June 9th (it only lasted 3 days). My question is, is this baby his if its due date was March 9th? I was always told you ovulate 2 weeks after your period, so I would assume it would be somebody elses baby.

Sometimes dates aren't exact. Assuming you've been with other people since or else you wouldn't be questioning it the only true way to prove who the baby's father is would be to have a DNA test done. There are times that you can have your period and still be pregnant.