Why has my baby lost weight?

My baby was having 5 bottles a day but he is sleeping through now and has subsequently dropped one bottle which he was only having 2 ozs of anyway. Before he droped this bottle he was having all 7 oz bottles and he weighed 17lb 3oz ( he is 13 weeks old and 9lb 7oz born) so as he dropped one the hv told me to up his bottles to 8 ozs which i did and i gave him a 9oz before bed as he is sleeping 11 hours. I took him to be weighed this week and to speak to my hv because he seems to be constantly hungry all day he drains all his bottles and still wants more. She was a different hv and she told me i am feeding him too much and not to give him any more but in one week he went from 17lb 3 to 17lb 2 after i have upped all his milks is this normal?? I have a nearly 4 year old too and he was a hungry baby but this didnt happen to him!!!