Help please

I had an ultrasound at 8w4d... they said they saw nothing... now today my hcg levels are at 20,000 about( they are rising) I’m supposed to be 9 weeks. I still have all my pregnancy symptoms and no signs of a miscarriage... my GP thinks it’s just maybe to early to see anything idk what to think... has this happened to anyone else

Update... I ended up in my local ER on Saturday in pain... Sunday got an urgent ultrasound that showed an ectoptic pregnancy and I got my tube removed since it was about to rupture... I have also filed a complaint against the ultrasound tech last week as did my OB and the ER doctor they were appalled that they missed it... thank you all for commenting and trying to help