i have recently started fostering a 1 1/2 year old pit bull from a rescue center not far from my house. i have taken him to the vet because i have noticed a yellowish green discharge from his nose, with a small decrease in appetite, a small sign of depression, and seams very weak. They have told me it can be the on set of distemper or a very server upper respiratory infection, is there any way i can know for sure which one it really is? I have really fallen in love with my dog in the past month and a half that i have had him. can anyone PLEASE HELP!?!?!