Should I go to the doctor or wait?

Hey everyone! So it's almost September, and my period was due the 25th. It still hasn't shown up. I've never been late before. I did have unprotected sex so I tested on Friday the 28th 3 days after my missed period. I got a negative. I waited to see if my period would show up, but it didn't. I tested again this morning, still a negative. Should I test again in a couple days, wait to see if my period shows up or should I go see my doctor?? Thank you all(: