Late period...

I'm on the pill. I took my last one for the month last Wednesday and was supposed to start my period last Thursday. Here it is the following Thursday and no period at all. I took a pregnancy test Monday and it was negative. I'm supposed to start my next pack of BC today but if I am pregnant, will it hurt the baby?? Please respond ASAP! Why is my period not coming? Last month it lasted 2 days total. Husband doesn't think I'm pregnant but I don't know what's going on. I am usually pretty regular.