Hello, If you had a positive urinary test and now you have a negative BHCG blood test then very likely you had an early miscarriage especially if you had bleeding and lower back pain. This is a very common thing and most women interpret it as a late menstrual period if they did not have the pregnancy test to confirm that actually it was a pregnancy. I would recommend you to see your doctor if you think you are bleeding more then usual, this is to make sure you are not developing anemia and to make sure all is well with your womb. A CBC and a vaginal ultrasound might be ordered in this case. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Antoneta Zotaj, General & Family Physician