I'm 30y old.period 20 days late, i have bad lower back pain,frequent urination and ovarian pain and pregnancy test is negative. what could it be?

Serum pregnancy test: Have you had a SERUM pregnancy test? Have you performed a 2nd home pregnancy test? Have you had a urine analysis done to look for an infectious disease? Have you called your OB/GYN or PCP yet? The last questions is probably your best hint at getting positive action since all WE can do on this network is what you're doing- guessing wassup with very little information at our disposal....Good luck!