I think a lot of people are confused about the whole foremilk/hindmilk thing. From what I understand, the milk is all the same. It is more watery at the beginning because the fat is stuck deeper in the ducts. More sucking draws out more fat with the milk. By staying on the same breast, you are drawing that fat out, and your body should make what he demands no matter how you want to feed. It just needs time to adjust if you're making changes.
From 4-6 months, babies do not gain weight at the incredible rate they did in the first 3 months. They start slowing down slightly. Kellymom.com says that infants 0-4 months should gain 4-7oz per week. 4-6 months should gain 4-5 oz per week. But think about how many variables there are. Different scales, different clothes, diaper on/off, just pooped a ton, has/hasn't eaten before weighing. You could really "tip" the scales if you were trying. Instead, I'd want to look at your baby and see - is he happy? Is he sleeping ok? (now) Is his output ok?
My dd was a "slow gainer" and I got so sick of people telling me how tiny she was. She was just meant to be petite, and she still is petite. She knows when she is hungry/full too. I nursed Max the exact same way and he is huge. Just a different baby.
You know your baby ... try not to get caught up in the weight gain game the doctor is making you play. Is it possible to switch HVs? :roll: