Had a dietician appointment last week (due to CMPA), she has planted the seed in my mind and now I'm constantly doubting myself 
My DS is 17 weeks old and weighs 12lbs. He was 6lb 9oz born and only dropped an initial 4% which he gained back quickly. He has never lost weight since then.
The dietician was looking at his growth charts and said she is concerned as he's gained weight, but dropped another centile line. He was born on the 9th, then gained weight but dropped to between the 9th and the 2nd. Now he has gained weight again, but has dropped to the 2nd. His height however, is on the 25th centile. She said that's what concerns her. I'm now watching his feeding behavipur like a hawk. He's on Neocate LCP and really doesn't drink much! He has 2.5-3oz every 3 hours, usually 4 hourly at night. Once he's finished, he is finished. There's no way I can make him take more than he wants! He pushes the bottle out of his mouth and won't take it back - he is obviously full! He does finish 5oz right before bed but that's the most he ever takes in one sitting. My theory is, because he was breastfed up until a month ago, he has a better understanding of when he's full? And has become accustom to feeding little and often?
So on a good day when he's taking 3oz max throughout the day/night, plus the 5oz bottle before bed, he's having 22oz over 24 hours, is this enough? He's also having plenty of wet/dirty nappies and seems satisfied between feeds.