Pregnant but no fetal pole?

I am 7 weeks pregnant today. Last Thursday I had my 4th ultrasound, and they found a gestational sac, a yolk sac but no fetal pole or heartbeat. My levels were doubling, and they are 49,000. I did the math according to my last blood work, and they should be about 100,000 now,..but someone told me at a certain point they stop doubling. Has anyone ever heard of the fetal pole showing later on in the pregnancy? Im so worried. I FEEL very pregnant, even bloating some.