I'm 2 days late for my period and I took an EPT test. It was negative but I swear, I don't feel like I'm going to get my period. I'm 20 and my period has been starting exactly like it should for the past 7 years. I can always tell the exact day!! What the heck is going on? When should I re-test?

I went to the doctor today and I'm not pregnant but my period is a week late. I have a gyno appointment for next Tuesday. Does anyone have any clues as to why I'm not having my period?? I'm not stressed or anything. Everything is the same except no period!! Can someone whose gone thru this tell me what is wrong??