Hi all im wondering if anybody has any advice f...

Hi all im wondering if anybody has any advice for me, my 1 month old baby boy is eating 120ml of formula milk every 2/2.3 hours during the day and 1 feed at night, i am scared i am over feeding him as he is gaining alot of weight, now 5kgs, doctors and midwifes have said if he wants it give it to him, so i have been demand feeding him. Has anybody heard of formula thickener????i heard a bit about it and just wondering will this help if i add it to his milk??? Cheers Vanessa