Help for Proffesor Budsworth (Buddy)

I dont like asking for help....but I am asking for help for Buddy. ...
Hes 12.5 years old and the best dam friend I've ever had and I cant picture loosing him.

Hes been having issues walking,  a few weeks ago he couldn't wlak seemingly over night. 
I took him to the vet and they put him on some meds...it seemed to help, I saw drastic improvements in just a week he was walking again.

Then one Sunday I left the house for a few hours, came back and he couldn't move, again.
He started throwing up and breathing heavy all night.

Back to the vet.
They think he had a bad reaction to the rimadyl medication.  So they switched him to prednisone.
It seemed to work over the next week.
Then all of a sudden it stopped and he couldn't walk, again.  

Back to the vet.

Now he got sores on him from laying down and some have opened up and hes bleeding.
I'm at the ER vet now on xmas eve. 

They are now  saying he has an infection and a fever and  pneumonia and needs oxygen and antibiotics.
Also, apparently hes lost 14 lbs since his first vet visit even with me trying to feed him as much as possible (whole milk, pb, oatmeal, dog food, treats,  etc.. 

I've already spend over 1500 I'm not sure how much more hes gonna need. 
They are recommending oxygen and hospitalization if he gets worse with the estimate at 5k.

Buddy needs everyone's help. If you've ever met him and  hes been a part of your life  or even  met in passing for a brief moment, I'm sure he put a smile on your face.

This is def not how I pictured spending my xmas.
Any amount would be much appreciated as I dont have the means myself.

Buddy needs you guys, I need you guys.
I cant loose my buddy.
Please help.