As in men's pants' size? Definitely *not* fat. Probably on the thin size...28 inch is an XS for men, or even an XXS. For a woman, at her natural waist? Getting rather large.
I don't have as good an idea about men's waist sizes as I do women's. I doubt you're fat though.
I'm 5'10" weight 150... and waist between 30 and 32... Not fat