Multiple Miscarriages (3) no pregnancy thus far?

I have had 3 previous miscarriages no children thus far and am currently 9 weeks 3 days.  All 3 miscarriages were in first trimester.  One of the first two miscarriages I was able to pass the fetus and it looked to be maybe 11 or 12 weeks.  I was a smoker back then and did not take very good care of myself however, for the past 3 years or so I have not smoked and had a miscarriage a year ago and now... I'm currently pregnant.  Anyways, the Dr.'s say that everything looks really good at 9 weeks which is great and they seem to think that everything should go well.  However, I have been through this already 3 times and I just don't think I will feel that way until I have a baby in my arms. I have been on prometrium 100 mg/ day since week 6 and baby aspirin 81mg/ day since week 8.  I feel like there is something wrong with me and I just can't have kids... I have not had all the tests but honestly I feel like within the next 3 weeks that something will go wrong and the heartbeat will stop.  I don't know why this happens but there is nothing that tells me anything different.  I hope for the best of course and keep praying for just one.  I have a tilted uterus and am not sure if that is causing the problems or what.  Any advice or info on similar instances?  What is the average time for miscarriage??? Why does the heart stop beating all the sudden?  I have the heartbeat around 178 at week 9.