I need help!

Malee
Guys, I'm really scared. I had unprotected sex on the 9th of July, but I took the after pill. I have made 4 pregnancy tests and all of them came out negative. And I still haven't got my period!!!! I don't know what is going on. I'm freaking out. I just want to see my period coming and there's none!! I don't know what to  do! 
Have any of you guys experienced this kind of situation? 
How long was your period gone?