alternator, battery or /

I put a new battery in the 94 Grand Cherokee in July but recently the car has acted like the battery is bad. I charged the battery and it started fine then took a short trip and needed a jump start. When I sit at idle and turn on lots of electrical things like the rear defrost, radio, defroster, lights on high beam, etc. the battery gauge indicates a heavy drain. When I begin to turn things off the gauge runs in the more normal position. I don't know if I;ve got a bad battery, a bad alternator or something else. Thanks for the help. Dennis