It sounds like you device is leaving all applications you run open until you reach capacity as opposed to closing them.
- Removing and re-inserting the battery SHOULD resolve this. If it does not, we know the is a more serious software corruption. If it does resolve this for a bit then the problem comes back, it is either due to a setting changed or again a software corruption.
I am not familiar of any setting in this phone that would disable automic closure of an app after a certain time but to be certain you can ask LG at 1-888-542-2623.
If all else fails you can perform a reset to factory settings, LG should be able to give you those steps and the required security code as well.