What Can Cause Delay In Periods,back Pain And Abdominal Pain?

Hello,I am 27 years old. Its been 5 days, I missed my periods. I have pain like I always have on starting of my periods like lower back pain, abdominal pain. My pregnancy test is negetive and I think I am pregnent, but yesterday (on 4th day of missing period) moring I got clot in urine, I thought my periods are start, but that was the only clot, periods were not started. generally, my periods are regular, my eating habits are irragular and i am stress person. i just want to know I am pregnant or not.