I think you might need to go to the doctor! I dont know this for sure but with eptopic pregnancy's (a pregnancy that is stuck in the fallopian tube, not the uterus) a pregnancy test may not be able to detect the pregnancy hormone because or the displacement, or something around those lines. Is your back pain sharp stabbing pains in the middle of your back or is it subtle and goes away quickly? Another symtom is sharp pains one one side of your lower abdomen. If these don't apply to you try taking a nice hot bath and relaxing, just clear your mind. Then go to bed but dont watch tv first, just crash. Many times after doing this women start their periods the next day! Good luck and keep me posted!