Supposedly 9weeks but ultrasound says 7

I’m a bit worried . I have PCOS and my cycle is very irregular, I often get my period every 2 months. when I found out i was pregnant, I took 4 tests and all came back positive so I went to my doctor and got an ultrasound. my doctor said according to when my last period was, I’m 9 weeks.

when I went to the ultrasound, they could only see the gestational sac and the yolk no baby though. the technician measured the sac and said I’m more 7 weeks. she didn’t say anything else but I’m getting worried about my pregnancy. it’s the period of waiting for update from my doctor and the next ultrasound.

am I having a miscarriage?