Not seeing a heartbeat around 6 weeks

So my last period was June 20th I have pcos I got a negative test August 6th and positive on August 14th. I had a ultrasound 2 weeks ago and all we seen was uterus thickening and my betas were 313 today I went in for my ultrasound we seen the yolk sac and fetal pole but no heartbeat. My doctor done blood work and is doing another ultrasound the 11th. Has anyone else been thru this I’ve had no bleeding and I still have morning sickness? My doctor said it could be early or it’s not a viable pregnancy.