For me, Summer is a big time to start more becoming aware of what I consume and when.
First thing I need to do is maintain my blood sugar throughout the day. That means eating healthy and enough, but not too, much food every 4 hours. High protein, low fat, high fiber is a good way to think about it. Prepping your own food might be a good way to get around eating whatever is available.
Second thing I need to do is consume water, which is something that you're doing. In that consumption you need to be aware of your electrolyte balance. If you're drinking a gallon of water or more a day, maybe you should put some oral rehydration salts for every half gallon of water you drink if you are feeling over heated. (Trioral is the brand that use if I'm doing medical responding for heat stroke in a place where there is a garbage can. There are also pellets that I use when I'm in a wilderness environment. I can't remember the brand, but they come in a bucket and they work great.) As far as drinking Gatorade goes, stop it. It causes blood sugar spikes. It is a lot like drinking a Sprite. Same sugar levels. Gatorade really doesn't have enough "electrolytes" in it to make it worth it.
The third thing I do is eat spicy food. I know that sounds counter-intuitive, but it works well for me in hot weather.
If you spend 2 hours prepping food and water throughout the week... I'd bet you start feeling better immediately. If you'd like to know more about what I do. Shoot me a message.
