11 month old son,, is his weight ok?

my son has always been a slow weight gainer ever since he was born, his birth weight was 7lb 3oz he is now 11months old exactly and weighs 17lb 8oz,, also about just over 27inches tall i don't think he will triple his birth weight by the time he turns 1 is this something to be concerned about? he is eating right and also still having 3 bottles of baby milk cow&gate a day so im sure he should be gaining loads of weight from that, he is eating everything i eat plenty of fruits and veg plus vitamin drops but just gaining weight so slow also he has been a bit slow on rolling over,crawling,sitting, saying mama and dada which he still don't say that often, he has only just learn to clap his hands wave and put his arms up plus he only just learn how to put one foot in front of the other only now and then he has no balance at all while standing, is this anything to be concerned about? he is healthy and the health visitor said he is fine but i just think he's a bit small for his age and not gaining enough weight hes not skinny he has a fair amount of weight on him like the chubby belly and legs so he looks fine could there be a reason for slow weight gain and growth? also he only has 2 teeth most babies i know at the age of 7 and 8 months old have like 7 or 8 teeth thanks