sounds like you have a draw to me. you need to check for a parasictic draw on the battery with a ammeter or you can use a test light. start pulling fuses one at a time till the draw goes away to find which circuit its on. maybe the hood lights on all the time or a glove box light stuck on something stupid like that usually happens. hope this helps.
What is the new battery that you got? I had a similar problem when I replaced my battery. It was found that my battery cable that was on the car,, the bolt that goes to the battery was too long and was not making a tight contact to the battery. I then replaced the battery with an original GM Delco battery and no problems ever since. Now it can hold a charge for 10 days, where before it was just a few days. Check that out first, could be your problem too. Good luck, Let us know what it was.