What I'd check on this dog is thyroid imbalance and possibly Cushings disease.
marvistavet.net/html/body_hypothyroidism.html
www.marvistavet.com/html/body_cushing_s_disease.html
Labs are well known for problems with both thyroid and adrenal glands particularly when they are seniors. The kind of symptoms you are seeing could reflect either of the problems but thyroid in particular. Thyroid issues can trigger a seizure in some dogs too.
I'm not sure the med mix is right for your dog or why your vet would choose one med over another but then I can't see your pet either.
The meds could cause fluid gain giving you some of the symptoms. The Deramaxx can cause a seizure.
If you are not happy with your vet's help with your pet you may want another opinion where the dog is examined by a veterinarian specializing in small animal internal medicine. This site may help you find one
http://www.acvim.org/Specialist/Search.aspx
I can't know what you have or have not researched if you don't give the information.
You can see your dog and I cannot so comparing the detailed data on the web to what you see is your best bet in deciding if you want another vet to examine and decide on treatment for your dog rather than working with your current vet.
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