what is wrong with my dauchsaund

our dog has always been overweight, but last spring she started doing odd things like licking the rugs and always wanting to eat and drink all the time, we took her to the vet and ruled out diabetes,but they thought she had cushings disease but then they didnt think she did,in time she went back to her old self,but now she has started peeing in the house and wont eat very well and is losing weight and doesnt seem to want anything to eat except human food,also i would like to mention she is very nervous and shakes all the time,do you have any idea what her problem could be,we dont know her exact age, we got her 9 years ago,our groomer thinks she is between 12 and 14 years old.

Try a different vet. You could use a second opinion.
   
Call around to local vets; ask to speak to a vet technician, & ask them what kind of modern equipment they have: do they have any digital machines or laser machines? Go to the vet with the high-tech machines; that practice will be more expensive, but they'll be totally up to date.
   
(And this post belongs in dogs, not Small Pets, which is for gerbils, hamsters, & the like. No wonder nobody's noticed it.)