eam will soothe his sore throat and airways.If his nose become very congested you can use sterile saline to loosen the thick mucous and remove it. He won't like it but it will help him breathe and be able to smell his food better. You can also use sterile saline to remove eye mucous if it accumulates.You can use Chlorhexidene oral rinses (like CET rinse) on the ulcers to keep them from getting infected by bacteria secondarily and keep them from becoming crusty and more uncomfortable. Some lethargy is understandable, let him rest as he needs rest to get better. If you can keep him inside until he is back to his normal playful self.If he runs a high fever (more than 104F), has a green or yellow nasal or eye discharge, stops eating even with coaxing and clearing his nose and eyes, or starts coughing or having difficulty breathing then he needs a veterinary exam. Not an emergency as long as he is eating but soon if he isn't eating or has a green or yellow nasal or eye discharge. If his extreme drooling continues then he probably needs fluid therapy and pain medication from your veterinarian. Sometimes these upper airway infections turn into pneumonia so that's what we need to guard against. In most cases antibiotics aren't needed and can contribute to a decrease in appetite so I don't tend to prescribe them unless I feel there is evidence of a secondary bacterial component. These include a green or yellow eye or nasal discharge, evidence of pneumonia upon listening to their lungs or an infection that lingers beyond the normal 7 to 10 days. I highly recommend testing him for feline leukemia and feline immunodeficiency viruses if his symptoms linger. These immunosuppressive viruses will make a simple infection much worse as they stop the immune system from fighting infections the way it was designed to do. If he isn't much better in 7 to 10 days he needs a veterinary visit. Here is a link if you want to read more about Calici virus: http://www.pet360.com/cat/health/calicivirus-in-cats/42gJj403b0idm8v6BjfOiA Let me know if you have any further questions.