Felicity is about 2 years old, and she's very healthy. She was fixed about 6 months ago, and has recovered wonderfully, she has a good appetite also, but she's not gaining weight! She's only about 5-6 pounds.. but I mean she's TINY!!! Her sides are sort of indented.. you know what I mean..? And she just won't gain weight.. the vet says theres nothing wrong with her, but I'm worried about my baby not gaining weight. Should I be concerned?