Nutrition for very active 9 year old with low blood sugar and exhaustion

[tinkerbug]

DS has been off school today. He's been not quite right for a couple of weeks since suffering from an ear infection which he was prescribed antibiotics for. Since then he has been feeling cold all the time, very tired generally, and yesterday ate barely anything.
Seen doc today who said its nothing sinister but he is wiped out and he probably has low blood sugar due to not eating. He is already v skinny and hasn't got any weight to lose, and is very active (swimming 3x per week and loads of football whenever he can!)
In the short term doc said calpol, isotonic drinks, biscuits and whatever food we can get in him.
Long term I think we need to improve his diet, he has always been a very fussy eater (apart from 0-6 months when he was a boob monster!) but now is v low on fruit, veg, calcium and could do better on good quality protein.
So......what would you feed your very active child? Any tips?

My very fussy (and always has been) 14 year old gets a daily multivitamin (well it isn’t daily but when I remember!)
Might be worth trying those nutritional milkshakes in Boots?
Hope made chicken nuggets? Shallow frying in oil would up the calories?
I feed him the few veg he likes - carrots and broccoli.
Pizza.

Thanks for the reply. He has a daily multivitamin already. I might look at some of the shakes from Boots, I don't think he's eating enough calories overall.
Veg he will eat are sweet potato, cooked carrot, and parsnip. And yesterday said he would eat beetroot! He gets at least one of these daily. Also a glass of apple juice and a couple of packets of bear yoyos or bear paws (a dried fruit snack) - as these are the only way I can get any fruit into him!!

Does he like yoghurt?

Full fat or Greek yoghurt is very nutritious, lots of protein and calcium. Served with honey, jam, granola or fruit. Even better if it's live yoghurt as this will help his tummy recover from the antibiotics.

Peanut butter on buttered toast.
Eggs any way (including pancakes).
Nuts.
Home made flapjacks with added desiccated coconut.