I have the opposite prob - with my dd weighing only half of what ur son does and they're almost the same age. But i know she eats heaps of healthy food and does not looks skinny or anything so i just have to accept that she's petite..under 70cms with a small frame. Each child is different so sometimes we just have to accept that if they're not where they're supposed to be on the charts - that's ok..as long as they're happy and healthy. U sound like ur doing all the right things