Heat exhaustion? prevention?

I have several medical conditions (heat intolarance, and diabeties insipidus, orthosopic hyptension etc) and I just moved into my own place. I love it and it is ADA and run by the university I live at it takes me about 20 minuates by electric scooter to get to class. I have an unbrella and a water bottle but to day I still spent 4+ hours outside and am feeling extremely ill. I'm hot nausious my PB is high, I have a headache and I can stand up without feeling I like i'm going to faint) this is going to be my shedual for the entire summer. I can't feel like this every night? what else can I do to help me? what can I do now to make me feel better now? thanks