I would be concerned that he has injured a tooth in his mouth or possibly has an object lodged between the teeth. There are other causes which includes oral ulcers and infection or even clogged salivary glands. I would definitely have a veterinarian examine the mouth closely for any of the above. He may need treatment with steroids and antibiotics or they may find that everything is in the clear, but this sounds like an awful lot of drool for it to simply be nothing. Especially with weight loss I would be somewhat concerned that his appetite may be decreased.
Please let me know if further assistance is needed.
Theresa
__________________
If I was helpful please hit
ACCEPT if you need more help just let me know.
In the case of an emergency please contact your veterinarian or emergency center.
Feedback is appreciated!