Much of what you are describing can be associated with low thyroid and in most cases holistic approaches do not work for this . It is also important to know that even vitamin herbs and minerals have side effects.
The fact that he is loosing his appetite is also concerning. This in addition to increased water drinking can indicate problem with the liver or kidneys. Other common causes of increased drinking are diabetes
, Cushings disease
( this can also cause panting) Addisons disease, urinary tract infection and in some cases cancer.
Panting and passing mostly at night can be signs of Canine Cognitive Dysfunction. This is similar to dementia in humans Click here for more on this
The trouble walking that you are seeing could be due to spinal arthritis , however if it is progressing then it is possible you are dealing with a condition called Dengenerative myelopathy Click here
Panting can also be a sign of pain.
Because your dog is already taking some holistic remedies I would not recommended any over the counter products. The only way to know how to treat is to know for sure what the problem is .
It may be beneficial at this point to do new blood work and perhaps consider a conventional approach for the thyroid if all other blood work is normal.I would also discuss the possibility of DM
I hope this helps and he feels better soon. Please reply back if you have additional questions.