I get smaller every time I take a bath. What am I?

Where I come from is not where I'm from; I'm only around when my source is not found. I am most active when you are at rest; You'll say it's dark but I'm doing my best.

I am white and sweet, a baker's delight, but devour too much and your teeth feel the bite.

I have many leaves, but I am no tree. I have days and weeks, but no time to see. I can tell you the future, but only for a year, Then you’ll throw me away when the new ones appear.

How do you tell if Lady Gaga is dead or just asleep?