Baby not gaining much weight

Hello,

has anyone's little ones not gained much weight since they were born?

My son was born 6/27 at 9lbs 6oz and at 2 months is only 10lbs 11oz. The first few weeks he was losing weight and we had our 2 month check-up yesterday and Dr said we will have to watch his weight. Not sure if he was not gaining weight because of his milk protein allergy. (he's now on soy as of last Thursday).

I'm concerned as my daughter was born 8lbs 1oz and by 2 months she had gained a few pounds already.