Why isn't my iguana eating or drinking (only iguana experts answer)?

my iguana who is 10 and a half inches from nose to tip of tail, is not eating or drinking. he looks dehydrated due to the fact that he has more wrinkles on his body. he eats but not a lot. i can see his ribcage. some times his belly is the right size but not always. and also he is turning brownish red from his pelvic area to the end of his tail. i caught him in the keys, if that info helps any. what should i do?!