Suggest Medication For Nausea And Dizziness Due To Excess Heat

My 16 year old, 230 pb, 5'11" son suffers with the heat. He is taking Prilosec for acid reflux, and Topomax as a migraine preventative. He cannot spend any time outside in the heat without getting nauseous, dizzy and refluxing. He used to be able to participate in lacrosse, running, etc., and feel sick at the end of practice, and recover after an hour or two's rest, but it has gotten worse. He feels sick after just walking from school to the car, etc. He seems to always be "hotter" than the rest of us. For example, we were sitting in an air conditioned restaurant last night, and he was wiping sweat off his face, and the rest of us were fine. He is only comfortable in a very "cool" room. When I take his temperature, it is normal, but he is flushed and sweaty. He is seeing a ped. gastolenterologist and a neurologist, but noone seems to know what to do about this. Whom should we see about this? I do not want him to spend his entire summer inside.