At my 3mth old's check he weighed 19 lbs now he is 5 months and i am worried cause he is even larger now?

he is now 5mths and weighs just the same if not more than his two and a half year old brother. Should I be concerned. His ped said nothing at the last visit. he eats approx six ounces every two hours, he will not calm down otherwise. he also has acid reflux and gerd which is the same but slightly different and he is on added rice formula. he appears to be a 8month old and is only five months. what can i do?