Carbol thickens the milk and keeps it in - but it doesn't treat any acid/ hearburn at all - and I do wonder if your LO is feeding so much and often becuase milk is a natural antacid.
Sometimes excellent weight gain can mislead people a little with reflux as they assume if is not bothering them when actually it is. Another sign can be babies who seem to prefer nigt feeds as it is easier for them to feed when sleepy - also they are more likely to want it as they have heartburn lying flat.
Was your LO big at birth as well?
But I think really the night feeds would be normal for a LO of this age and size, and in terms of the reflux you are the best judge as to whether it is part of the issue or not. If you do then perhaps a trial of an acid supressing agent would be worthwhile - so some Zantac is what is usually given.
