Worried!!

My LMP was 08.13.2016 well I went to the doctor 2 weeks ago did a pregnancy test it was negative this was exactly 2 weeks before my missed period well last night I got positive pregnancy test at home I rushed to the ER because I was cramping mildly they did a urine test came back positive then they did a negative pregnancy test it was negative and I had an ultrasound they couldnt see anything but he says its too early to tell by blood a few mins ago I took 2 more test and the lines were darker so am I really pregnant????