My brother's giving me his lizard but I don't know what kind it is & it's not eating right and has lost a lot of weight, so I'm kind of lost on how to help it. Anyone an expert with lizards?

Hi! I'm Ashley, 21 years old. I like to research, it doesn't matter what. I'm a book-worm, nature and animal lover, I like researching J.R.R Tolkien's Languages such as Elvish, Dwarvish, Orcish.. (I wanna learn Sindarin, Elvish.) So yes, i'm weird. I have a few health problems some being - Cerebral Palsy, Epilepsy ect. I love Classic Rock & Motown if you wanna know more... Er.. Ask? Lol -Ash