A.,
I just reread, and I sound like I'm going off the deep end, but I'm not: I don't have time to rewrite though. Just know that my son is where yours is, and we tweaked his diet so he is getting more fat on a daily basis.
Don't worry, it gets you nowhere. :| Be advised by people you trust and work from there to get where your baby needs you to be as far as being informed. Remember: he's getting VERY active now, and will only continue to do so, and his intake hasn't caught up with his usage yet.
Where YOU need to be concerned: is his growth curve turning DOWN? You don't say how much your baby weighs - in relation to birth to now. If he has plateaued - not gained anythign significant or lost overall from his OWN curve - then you need to be a bit concerned and look at dietary intake.
My son gained little across the board on his WEIGHT (his height and head gained consistently) and ZERO 9-12 month mark. His doc is a bit flighty (I've noticed this, husband doesn't want to switch). She is all about charts, and totally overlooked that he was happy.
Is your baby happy? ARe you getting him a rounded diet (protein/carbs/fats/veggies?) Believe it or not, the fat intake is important, especially right now.
Has your doctor shown you the charts? Has he talked about WHY he's concerned?
There are things you can do (especially if you are holding off on Milk because of allergies or potential allergies) to boost his weight effectively and in a healthy way.
I'm going to guess your son crawls like there's no tomorrow, and is faster than some people running. :) That burns up a lot.
If you would like some ideas for how to increase fat in a healthy way, just msg me. I'm here most days. Most of all, don't worry, just be smart about your son's intake on all fronts, and he'll be gaining responsibly before you know it. He'll probably walk first though. ;)
Good Luck,
M.