Could I be pregnant or is it my endometriosis?

I was diagnosed with endometriosis last year and had surgery to help alleviate it. I was put on birth control and 5 months ago I stopped taking my birth control and my boyfriend and I were actively trying to get pregnant. Today is supposed to be my 3rd day of my period and still nothing. What worries me is I have some major tightness in my left lower back that used to bug me with my endo. I would be so happy if I'm just pregnant but scared it might just be my endo... I made an appointment with my Dr today. Has anyone else with endo felt this way?