low setting placenta

Has anyone had this issue? I had three losses last year. Two at 6 weeks and one at 4 mths. We are 5 days short of 5 mths right now and things are looking good. They said my placenta is sitting low, but not to worry because it's normal in some pregnancies. Well it has me worried. We lost our daughter at 4 mths due to a tear in my placenta. Any words or advice would be great.