Pregnant?? Help please.

Is it possible to be pregnant if I had a period March 4...and an HSG test to check my uterus and tubes on March 12. I went for my usual blood work yesterday to see if I ovulated this month and my progesterone levels were much more lower than what they normally are. I am taking Clomid. So my RE doctor put me on Progesterone and estradiol  to protect me because he thinks I might be pregnant. I do have PCOS. I have to go back next Friday to check my blood to see if I am pregnant. So I am all over the place but how could that be physically possible if I had a scan on March 12. Wouldn't you see a baby or something in my uterus?? Or at least a dot. I mean I would be over the moon excited if I was pregnant but I do not want to get my hopes up. I just do not see how I could be. Has this ever happened to anyone??