Low Calorie Snacks?

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What is low in calories that is also filling?
I have a chronic hunger problem, even though I will have already eaten, and I drink lots of water (within a half hour of eating anything, I am hungry again, but obviously I can't constantly snack).
So yeah, any suggestions?
(And yes, I've been to the doctor about my chronic hunger issue, I was told it was a hormone thing, so it's kind of like fake signals that I'm hungry and need to eat, not that it's in my head or anything).
Tips much appreciate as to low calorie snacks that are filling.
- JECA