Pregnant or not

I am 7 days late. I did 3 home pregnancy tests, two were clearblue. They all tested positive. When I went to the doc to confirm, he said its not possible because my uterus lining is not thick enough. Its only 11mm instead of at least 12mm. Asked me to come back in two weeks time if I had not had my period . now I am confused. I don't know if I am pregnant or not