I Had An Ultrasound Done About 3 Weeks Ago And

I had an ultrasound done about 3 weeks ago and the results say that my Uterus is thickened to 20mm and i am late on my period by 2 weeks and i have taken 4 pregnancy test and all are positive. So is the thick uterus giving me false test or am i pregnant and the thick uterus is harmful.