Battery goes dead over night?

I replaced the battery on my 1991 honda civic about 3 months ago with a new one from o'reillys and it's been good ever since tell now about two days ago I didn't use the car at all through out the day then the next day tried to turn it on and nothing the battery was completely dead so I recharged it thinking I left something on prabably and used the car like all day yesterday and today I tried startin it and the battery is dead agian not completly dead but it's not enough to start the car now can someone please let me know why this is happening I don't leave nothing on and the car is completely off?
Please and thanks need yours answers

You must have a drain on the battery overnight, is the glove compartment light shutting off or the boot light staying on and the clock is also a drain, if all three are draining the battery overnight i would say it will be flat.

It's possible you could have an alternator issue or it is possible you could have a bad battery. If you've only had your battery for 3 months, and it's actually the problem there should be a warranty on it to replace it.

What you can do is check or alternator and if the alternator is busted then you need to switch tht and you will be fine if tht dosent work then try to change the battery

Your alternator could be shot and is not recharging the battery as you drive, so is just draining it. That's probably not the case though if you are stopping it and restarting it several times throughout the day, since a drive of any real length should drain a battery.

Have you done anything to it electrically recently? Hooked up accessories or the like that might have been done incorrectly?