Could I be pregnant????

Could I be pregnant???? I had my last Cycle june 11-19 and a doctors appt. on June 22 they test my urine and said it was blood in my urine they were testing for uti but the test came back negative however I had unpretected sex July 14-31 every other day my cycle didn't come at all on the 1st and 2n of august I had light brown tarnish discharge and moderate back pain and cramps I keep taking test they all come back negative help me out I don't know what's going on. How long should I wait to test its been a huge change in my appetite I only eat like ones a day.