Elderly Border Collie quivering and incontinent

I have had my 15 yr Border Collie since puppy hood. Buddy is a big part of my life.
He dislocated his hip 1.5 yrs back, so I have to carry a 48 # dog everywhere he goes.
A wheelchair didn't work very well and Buddy is able to walk at least some. Enough
to do his business anyway.

He was diagnosed with vestibular disease (doggy vertigo). Which I believe is why he
injured himself. He now has started to quiver and I'm concerned that is from pain
and other factors, like old age. He was given pain med for a couple of months after
the hip diagnosis. I don't think they helped very much and were costly.

Last couple of weeks he has developed bladder control problems. Any suggestions
to help with his quivering and incontinence?

Aww, poor old boy - it could be one of many things - a reaction to the medication, some nerve damage, or lack of muscle control elating to the hip injury. I think only a veterinarian can figure this one out, sadly.