Do I need to buy a new battery?

I drive a 1995 Nissan Sentra and tonight when I tried to start it up before work the engine wouldn't turn. I jumped it and was able to drive to the gas station, turn it off, turn it on and go to work. After work, I tried to turn on my car and it wouldn't turn over, so I jumped it again. Prior to this excursion, it had been sitting out in my driveway for several days, untouched, in this cold icy weather. I was wondering if I need a new battery or if it is just cold? Being a broke college student around christmas, I would rather not buy a new battery if it is not necessary. Any insight would be greatly appreciated!