freaking myself out

Jay
Going back to August, my husband and I went to our first appointment at 7 weeks. Heard a heart beat of 127 and doctor said everything was great. I start bleeding at 10 weeks, go back in and there's no heart beat. The doctor told me there's no explanation but more than likely a baby has a heart beat then doesn't because there was a heart defect.
Fast forward to last week. I'm 6 weeks 5 days and I start bleeding, go in for an ultrasound and baby is fine with a heart beat of 128 bpm. Now I'm 7 weeks 2 days and I'm looking at other people's sonograms who are where I am and the heart beat isn't under 140 bpm. Does it speed up with time? Am I just paranoid that this is going to happen again?