Should I be worried?

At 18 weeks I was told I had placenta previa at the ER (went in due to bleeding), has a follow up appointment 3 days later and it had already moved, but was in the front (anterior). At my 20 week scan it was moved in a normal position. Had some heavy bleeding at 22 weeks, I was checked and now my placenta is less than 2cm from the cervix opening, so I was told I had previa again. I have another scan in 2 weeks (24 weeks) to check to see if it has moved. Has anyone ever experienced this?