Late period?

Shania

My last period was Aug,19th 2017. It’s now Sep,27 2017 and I still haven’t started. I was sick 2 weeks ago and made a trip to the hospital so I could be cleared back to work. They had me pee in a cup and did a pregnancy test it came back negative. But I still haven’t had a period. Anybody have any ideas why? Btw before my period on Aug 19th my period before that was July 11th.