My Period is late 8 days, mild back pain, tubes tied 6 years ago, took two pregnancy tests both negative.....

a little over a week ago, I felt a pressure inside my , almost felt as if something was coming out-lots of pressure, no pain. next day, right back pain, that continues to this day- I took an over the counter AZO test, came back positive, so I figured a UTI, but I had no other issues. My period is 9 days late, I took 2 pregnancy tests both negative, my tubes were tied 6 years ago. I am always on time 28 to 33 days. I dont feel as If I will get it- I am not under stress. and have no other know health issues. I have a dr appt in 3 weeks- but until then I worry about Eptopic pregnancy(I was told they may not show on a test!?!), I question Tyroid issues, Cancer, tumors? Anyone offer advise and know what this sounds like? Thanks