I would consider this a pressing matter, Jo. I would highly recommend a vet visit. Anytime that a pet is lethargic, not acting himself, is not wanting to eat, etc. These are all signs that your pet needs help...especially if you're seeing these signs after having dental work done. The masses could be anything from abcesses to enlarged lymph nodes...or actual tumors (although having them on both the left and right side at the same time is unusual). The fact that they've come up so quickly after having surgery done on the 9th of July is even more concerning. If this were my pet, I'd try to schedule an exam with your veterinarian today. Further problems that your pet can have aside from the masses under the jaw would be organ/metabolic damage from not eating for a prolonged period of time. The chances that the stools are unrelated to the masses you're seeing near the jaw is fair. I would suggest having a fecal analysis done on your pet's stool to see if he is positive for intestinal parasites or protazoan. As well, the frequent urination could be due to age. I would suspect that the reason that your pet probably holds his leg up after the urine stream has stopped is because there is a delayed reaction between the brain knowing that the bladder is empty and the time it takes to replace his leg on the ground. However, obtaining bloodwork (which would also be a great idea since your pet has not been eating and you would want to make sure the liver and other organs had not been damaged) and having a urinalysis run would be the best way to determine if there is something underlying that could be causing a necessity to urinate frequently. It's better to assume that something is wrong than to just assume that old age is the cause.
Good luck! Let me know if I can help you further :)
Sami