My daughter just had 3 positive pregnancy tests, she went to the E.R. for cramping in her lower abdomen, they?

my daughter just had 3 positive pregnancy tests, she went to the E.R. for cramping in her lower abdomen, they ave her 2 ultrasounds and sdaid they cannot see any fetus in her uterus...it may be a tubal pregnancy, is there any way possible the ultrasound may be wrong? shes like 3 or 4 weeks , her hcg levels are going up...and shes not in any sort of pain at all right now...im very concerned about her ..please help