? about my rabbit that is skinny?

hi there i have a rabbit that is very skinny but eats and gose to the bathroom normanly she drinks water all the time and has alot of hey it always gone by morning is there anything with the weather change doing this i dont think she has worms or anything like that cuz i checked her over for missing hair or scabs or bugs she has none of that im taking her to the vet tommorw but i havent sleept in days i hope its not deadly i just want to know iff any body else had this problem ive been useing cardboard and newpaper for A week now due to not having the money for bedding all my other bunnys are fat and healthy shes always been small cuz shes a lop so what is the right waight for a holand lop? thanks for all the help all of u have givin me