'96 Contour battery problem

Here's the story. I bought a brand new battery a few months ago and one of these cold New York City mornings I go out to start the car but nothing. It didn't even turn over, wipers come on slowly and that's it. Just days before I checked the alternator with the guys from AutoZone and it turned out good. Also I checked myself for all the electrical shorts and all was good.
Ok, I figured what else but the battery again. Why? No clue. Maybe it's a bad one, so I went back to the PepBoys and got the new replacement, put it in and after minutes of cranking finally somehow I cranked it up. I don't know why it took so long to crank it up but it did. It was good for two months and yesterday again, the same thing happened. It was two cold nights and I wasn't using the car for two days just like the first time although not that cold this time. Anyway, I had to get the jumpers and start it up.
Now I'm really confused. Should I replaced the battery again or it could be something else. I have the fear every day now that I'm not gonna be able to start it. Please help , I don't know what to do!

Sounds to me like something is draining the battery. Maybe a clock, radio, etc.... When you drive the car everyday, the alternator keeps the battery charged and when you let it sit, the battery dies, something is definetly draining it.