I was diagnosed not that long ago also, so I really understand your concern and frustration.
ALthough some will argue for my guts, what I eat has a big impact on how I feel. In the heat, you need electrolytes. These will keep you stable. Hoever, the way you are getting them would make me sick. All that artificial ingrediants and suger. My stomack starts to hurt just thinking about it.
I am cycling fairly long distances so I work in the sun also. I use a product called ELETE. It is a liquid concentrate of electrolytes. I add this purified water. If I am looking for carbs I add some knudesen's pure juice or welshes grape juice. Both have no suger added and are easy to digest.
I use 4 parts water and 1 part juice and ELETE and I have home made natural gatorade my guts can handle and everything I need for the heat.
Steriods can make you sun sensitive, I use UV protective clothing and sun screen. I would also use a base layer. Clothing that is designed to wick moisture away from your body so you get the most intented cooling effect from sweating.
Hope this helps and good luck