Where is my Period?

So My Period has totally Skipped out on me this month was due on the 6th of this month and nothing.Cycle day 54 today.I took a few pregnancy test when i was about 2 weeks late all neg.Did a Ultra sound and the Dr said that there is a thick line.So i dont know if she would have missed something.I havent tested again.I just thought My period was really late and because i did the ultrasound i am def not preg.Has anyone else had an experience like this?