Missed twins?

So at 3 weeks 3 days my hcg was 54.8 at 3 weeks 5 days my hcg was 225.3 I immediately got worried and expected twins. (Mind you we thought I was further along hence the hcg draw but later found I was not as far as we thought.) at 5 weeks 3 days my hcg was 48,720 they did one ultrasound at 6 weeks 4 days found one baby with a heart beat and nothing else… I have an undying feeling I’m carrying twins, my hcg continued to climb and being that this is my 4th viable pregnancy I can’t say “oh I’m showing a lot” because honestly I never have showed a crap ton anyway. I am having tons of pelvis pain I’m feeling kicks now (im 18 weeks) and for a baby being a few inches long I feel like I’m feeling 2 kicking but maybe I’m making it up. I have my anatomy scan tomorrow did anyones doctor miss a twin at such an early ultrasound and later found 2? Maybe I’m crazy but I’m dead certain there is 2 in there I know my body pretty well. Lol and my doctor is not listening at all for my concerns.