Confused!

I found out on March 17 that I am pregnant. I have irregular periods and not completely sure when I ovulated. My last cycle lasted 34 days and the first day of my last cycle was January 31. I had my first appointment yesterday. Based on my last cycle I would have been “8-9” weeks however the ultrasound measured around 5 weeks with a yolk sac present. The doctor said I probably ovulated a lot later with my irregular cycles but not 100% sure. My Hcg level taken yesterday came back as 6,802 and the nurse said that correlated with being 8-9 weeks. I’m so confused and worried. I go back for a second ultrasound in a couple of weeks. Anyone have an experience like this and had positive results?