What the hec. I would think that if your heard a heartbeat this week when you did not last week that the baby is doing ok. I am not a doctor though. I think babies are a gift from god. I have lost one. Think positive and try to relax. If something is wrong with the baby your body will take care of it naturally. good luck!
Some times you don't see a heartbeat that early, that's why most ultrasounds should be done after 6 weeks. Do they mean baby is shrinking in size? If it is a miscarriage, then they would need to repeat the ultrasound in a few days, and also check your hCG levels to see if they're decreasing and if baby has stopped developing.
I am so sorry to hear that.. I don't belive the Doctors all the time.. They have misDiagnosed so many pregnancies and such. Keep your head up and stay strong. The baby could get better.. Just give it time.