6wks 4 days by LMP but no fetal pole on US

DH and I have been TTC for 8 mos. Its my first. I’m over 35 so started getting tested in November to see if there were any issues. My day 24 lab showed low Progesterone and day 3 lab under active Thyroid. I started Clomid at 50mg. Dec 11 (Day 16) I went in for a PCT test and they said Clomid didn’t work, as I showed no signs of ovulation. I was shocked to get my BFP on Jan 5th! Because of the previous test results I went in Jan 8 to test HCG and Progesterone. Jan 9 thyroid function, and today my first US. Test results for thyroid & Progesterone were normal and HCG was 11900. At 6wks 4days according to my LMP, at my US they found a sac in my uterus but no fetal pole. My doctor said it could be that I ovulated late and it’s just too early, or that it was an empty egg. He also saw blood around the sac but didn’t seem worried about it. I go back next Friday for another US. My cycles are very irregular ranging from 23-39 days. I’m scared but trying to be positive. Has this ever happened to anyone and the fetal pole was found at the next US?