Hello, So My Period Is 16 Days Late. I Am

Hello, so my period is 16 days late.
I am very regular, like if my friend is on her period most the time I catch hers. But I've been around friends on their period and I still haven't got mine. Monday 8-3-15 I started bleeding but not bad. I went to the hospital to see if I was okay. They did an ultrasound and seen something in there. But all my tests are coming but negative even my blood tests. I am having pregnancy signs. I just feel like if they seen something I should be able to stay in pregnant. It is Wednesday 8-5-15 and I have completely stopped spotting. What's going on with my body? Am I pregnant or? Could the test but wrong? What's going on... Please help me