I'm no expert, but maybe replace the sugar in the homemade gatorade with honey? Personally I've never reacted well to real sugar (I immediately feel tired and strangely I get a lot of phlegm in the back of my throat). The sugar may not be the only reason he is crashing, but my guess is it's not helping. Honey is great because not only does it have plenty of nutrients but your body processes it differently, which could have an effect on how he is feeling.

I have a recipe for homemade gatorade that I got from a beekeeping seminar I attended, but can't seem find it. I think it was very similar to your recipe, without the lemon juice and the honey replacing the sugar. Since you already heat up your mixture it would be easy to add the honey. Sometimes I like to add a little bit of raw apple cider vinegar for the health benefits & taste, but of course that's all personal taste. If you want to add a little pick-me-up, brewing some green tea to add to the drink might be a good idea for the caffeine.