measuring 10 days behind

Meredith
Hello everyone! I am driving my friends and family nuts with my worrying, so thought I would post somewhere with people who would understand what I am going through.
In February I had a silent miscarriage. I was 3 days shy of 12 weeks and I went to the bathroom to find the tiniest bit of spotting. I was also told at my 7 week ultrasound my baby was measuring "really small" at about 10 days behind, but I didn't think much of it, as my dr didn't seem to be too worried. 
Well,flash forward to last week, when I am supposed to be 8 weeks along with my rainbow baby. When I conceived I used ovulation tests, so I know I ovulated a few days late on may 1st, which would set my due date back about 4 days. So I go to the ultrasound and the tech tells me that the baby has a heartbeat of around 148 and is measuring "4 maybe 5 days behind" which is exactly what I expected. A few days later I received a message from my doctor telling me not to worry, but I'm measuring 10 days from my expected due date of Jan 18, and have an adjusted date of Jan 28th. I took a pregnancy test on may 10th and got a pretty faint positive and then again may 13th and got a really strong positive! If I actually ovulated later, it would have been May 6th, and there is no way to have gotten a positive test so soon. Should I be worried? I am thinking the heartbeat is measuring a week behind after a bit of research, online says the heartbeat should be at around 160-170 in week 8. Has anyone heard of a heartbeat catching up? I've been so scared ever since just waiting for the bleeding to start. 
Omg, what an essay! That you to anyone for their input, means a lot 😘