Especially if it's a Duralast battery from Autozone, test the battery first. It's nto uncommon for batteries to be defective right off teh shelf. Take it to an auto shop so they can do a load test, not the parts shop where you bought the battery BC their testers often show false negatives.
OTHERWISE...
Parasitic draw. Every car draws a small amount of current to keep memory in the stereo, run the security system, etc. Normal draw is up to 50 milliamps (.05 amps). Somtimes something goes wrong and creates greater draw.
If you have an ammeter, you can test the parasitic draw. If the draw is bad enough, even without an ammeter, you can test it. Disconnect the negative cable and barely touch it to the negative terminal. If you see or hear any amount of spark, something is drawing too much current.
With an ammeter: You need an ammeter that can test up to 20A DC. Smaller meters will blow their fuse or burn out if it turns out the draw is greater. Disconnect the negative cable. Connect the red lead of teh ammeter to the negative cable, connect black lead to the negative battery terminal. The ammeter will now show how much parasitic draw you have. If it's over 50 milliamps (.05A), something is draining the battery. With the ammeter still connected, start unplugging fuses to see if the draw drops. Start with what's most suspect, like aftermarket stereo or security equipment, then radio fuse, etc.
It's time consuming, but it can be done.