Should i join the Army?

I originally tried for the Marine Corps but i was Rejected. =( im going to try again but i have to wait. until then Im thinking about joining the Army but im not sure if i should. Im not happy having a normal job. Im a volunteer fireman but it is not enough i feel unfulfilled and that i should do more and be part of something bigger. I am 18 years old. And if i Enlisted i would want to be a combat medic or infantryman.