Can you get someone to help you look in his mouth? (Roll him in a towel, like a kitty burrito, friend holds the burrito kitty, you open kitty’s mouth). If he does have an abcess, then he would definitely need to see a vet. Dental abcesses can rupture and cause sepsis, which can be fatal. This the same for humans, dogs, etc.
And Patrick will tell you it is very challenging to get herbs into cats. Not impossible, mind, just very challenging.