I have had sharp pain in my lower back for 3 days, I am tired most of the day, peeing a lot more than normal especially at night, sometimes I am nausea , I am 4 days late for my period. Stomach hurts when I pick up my 21 month old son who is about 24 lbs. I stopped taking birth control in June. 3 negative pregnancy test . Could I still be pregnant or should I be concerned that it is something else?