Unsure Pregnancy

Patient: Hello. I’ve been taking the same birth control for the past 3 years and I’ve never missed a period. This month however, my period didn’t come when i was on my inactive pills. I took a pregnancy test and it came up negative. I was supposed to start my new cycle of pills this past Sunday but I haven’t to see if my period would come but it hasn’t and I’m already a week late. If its not pregnancy, what could it be? I have no symptoms of pregnancy except for dizziness and being light headed or faint.