ADVICE: AF 3 days late

I'm usually really regular and never late. I'm 3 days late but I'm still getting negative tests and blood count was negative too. The doctor told me that if I was to be pregnant i would of got a positive by now, so there's no way that I am pregnant.

So if I am not pregnant, then what can cause my period to not turn up? This isn't normal for me and I'm worried! I haven't done anything different! I'm just confused because I feel pregnant, but the tests say otherwise. The doctor was so rude to me and just told me there's no way I'm pregnant as the test would of shown.

Please comment x