Anytime im hot, i feel very sick. i feel nauseous, dizzy and like i am going to faint. when its cold out, i feel great. why is that? how can i fix it?

Could be normal: If this is how you've always been or can remember being then, it likely is the way your system has been calibrated by nature. On the other hand your doctor may consider checking parameters such as thyroid or your female hormones. They may even choose to recommend autonomic function testing if other information is present or get an MRI of the brain with contrast if certain information present.