Hello, and welcome.
I'm sorry Grey is not feeling well. The drooling could be caused by an oral problem like an abscessed tooth or gum infection or it could be caused by nausea. In addition, he may have chewed on, or ingested a non-food or toxic item.
Since he's listless, he may have an infection in his body which needs to be treated with antibiotics. He needs to be seen by a vet, asap. If he had a urinary tract infection or a blockage two years ago, I'm sure you're watching to see if he's urinating at usual.
For the moment, you can give him 1/4 of a 10mg. Pepcid AC (Famotidine is the generic) tablet to help curb his nausea, if he is nauseated and settle his stomach.
However, if he has an infection in his mouth or an infection in his system, he does need to be seen in person for a definite diagnosis and treatment. If you can get him into an ER vet center now, that would be best.
Don't forget to watch that he's urinating normally.
I hope all will be well with Grey!
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