Why do I feel so fat?

I'm not fat at all and I know that. I'm 5'2" and 101 lb. I feel really depressed because it seems as if I've gained 2 lb. I don't want that; I never want to gain weight ever. Nobody notices it except me. I also got got a few cm taller. But I just feel so bad. How do I loose 3lb? I'd seriously feel like killing myself if I ever go over 105.
Why do I feel so fat?
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