Check the label on your battery for the warrantee duration. If it's one year then this isn't unusual. If it's more than a year then it's very unusual but can happen. The only way to know is to test it under load
Link to load tester.
and test the water with a hydrometer
Link to hydrometer.
Places like Wal-Mart and auto parts stores offer free testing but it's only a voltage test and won't really tell you if the battery is functioning correctly. Take it to the supplier's rep and ask them to test it properly. If it's under warrantee you should get a replacement.
If the battery is good then you have developed a parasitic load you don't know about and you will need to test the storage conditions current with a DVM. If the load is high like over 5 AMPS then pull fuses until you find the problem. You could of course do this first and save a few bucks, but these two tools are a good thing to have in your tool box.