Issues with Doing Too Many Ultrasounds

I am considered a high risk pregnant, due to losing my first baby who had a heart defect after birth.
I am now 23 weeks pregnant and I was bleeding in the early trimester for two weeks so I had to be under close monitoring.
We have done fetal anomaly scan, fetal echo for the heart, in addition to 9 other regular ultrasound scans since the start of this pregnancy. 
My doctor keeps saying it is okay and doesn't cause any harm to baby, but my relatives and family are all very scared and they keep warning us telling there is no need for so many scans and we don't really know what effect they might have on baby after he delivered. 
I would like to know if there has been any proven cases where too many ultrasounds did cause harm to the baby.
We are very worried and concerned.