desk0
I hate to tell you this, but you have two issues you need to look into. You have a drainage problem when your car is off, and you have a low amperage problem when your car is on.
First, let's tackle the problem while your car is running. Most Parts places will test your alternator for free. Now it's possible that these guys want to sell you an alternator so if you have the ability to performa LOAD test, do it yourself. Otherwise take your car to two different places and see if they tell you the same thing. I think, from the info you have shared, that your alternator, or voltage regulator is starting to fail. A test from one of these places should help you narrow it down.
Now the drainage; I don't know your level of expertise, but there is an easy way to test for voltage drop using a multimeter. The meter needs to be able to handle a 10 Amp draw (most Flukes can do it). Make sure your key is off. Make sure your meter is set to an Amp setting and the leads are plugged in the appropriate place. Disconnect your negative terminal on your battery and place the meter in series between your battery and the negative terminal. Positive lead to the battery, negative lead to the cable that would normally connect to the negative post. anything below .02 amp draw is acceptable. anything above that will drain your battery .
Now the disclaimer: If you are not confident you can do this or if you don't know anything about electricity (electronics), Don't do it. Please leave it to a pro. I would hate for you to burn up your car and come back here blaming me.
Be safe man...