I get heat induced migraines. Can't increase metabolism without migraine. Need exercise! HELP!

I experience seratonin syndrome if I take serotonin targeted maintenance meds and take my Max Alt.  With every year that passes, I am gaining 10-15 lbs, which ups my blood pressure.  I just want to be able to exercise without a headache!! Even if I am in an air conditioned place, if my body gets heated up, here's the migraine.  I am partially convinced that it is a problem with my endocrine system -- a thermostat malfunction if you will -- but of course, I haven't found a dr. that doesn't just take my blood for thyroid function and of course, if it is in the "normal" range, it is assumed that everything is ok.  Whatever it is, I would like to find SOMEONE, SOMEWHERE, that is willing to take whatever test to get to the source so I can do something!!!!!  PLEASE HELP!