What Causes Delayed Period, Abdominal Pain And Lightheadedness While HPT Is Negative?

I was supposed to start my period on the 6th of this month, I havent. I have taken 3 store bought pregnancy tests and all have been negative. I am having moderate to severe abdominal pains on the right side of my body accompianed by fatigue, lightheadedness and some moderate nausea. Could I be pregnant or could I have an Ectopic Pregnancy?