My ferret i think is dying please help?

i have a male ferret bout 1.5 years..an he was healthy for a while an all of a sudden he became lethargic..an he would take like 2 steps an fall asleep..he has pucked a couple times..and his nose is a yellowish tint and hes gotten fat quickly..hes not loosing fur hes not itchy his nose is dry his eyes are fine..hes not fixed..an his balls look like he has a small bruise on each one..im gunna be moving him from my other 2 healthy ferrets to keep an eye on how much hes pooping eating an drinking on his own..when i know he has pooped its sometimes green slimy or its just plain diarriah..my boyfriend isn't back yet for a few more days an my parents don't have the money to take him in..im jsut trying to figure out wat may be wrong with him an he hasnt ate anything strange either...any advice would be nice