16 days late, testing negative

Hi I'm 16 days late. I was supposed to get my period May 29. I have never taken birth control pills or any hormones. I did have unprotected sex "pull out" with husband but we have been doing that for years without ever getting pregnant. I have had a regular period since 5th grade. I'm 27 years old. I have done 5 hpt and they are all negative. Now what? Left a message for my M.D. yesterday. What do you think is going on?