Baby tummy measuring small

So we had an ultrasound about a month ago and they said she was measuring small. Then we had another ultrasound last week and they said she is growing but her tummy is still measuring small. I'm on pretty strict bed rest and my next apt isn't for a couple weeks. Just wondering if anyone else had this problem. Should i be worried? She also had cysts around the placenta but they took me off my meds so those are going away. I guess I'm just stressed because this is my 4th pregnancy but the first 3 were miscarriages.