Late Period

Hi all! I’m on the combination pill and have been using it since mid-April. The last time my boyfriend and I had sex we used a condom and I was on the pill. I take it at a consistent time each day. I should’ve gotten my period two days ago (I’m on my placebo pill week). I haven’t gotten my period since July and I’ve taken three pregnancy tests (2 in August, 1 this month) and they all came out negative. I’m mostly just scared because I’m in my last year of college and absolutely do not want to get pregnant. I’ve been under a lot of stress lately so my diet and exercise routines have changed a lot over the course of the last two months. Is this normal? What should I do? Has this happened to anyone?