When I drink a lot of caffeine (full soda, cup of coffee 5 hour energy) I get a rash, it's hard to breathe, and I start palpitating, am I allergic?

Caffeine. Sounds like you are sensitive to caffeine. A rash can sometimes occur from boing nervous. There are no similarities in what you drink to indicate an allergy other than caffeine and that does not produce an allergy.