What Causes A Delayed Menstrual Period With Negative Pregnancy Test?

Hi I was due on my period over 2 weeks ago and nothing. I am nearly 30 and have never missed a period or been late. I am on the pill. I have also taken 2 pregnancy tests last week but both say negative. I have sore breats and my stomach is very swollen including the top part of my stomach. I am very confused and to be honest quite stressed about it.