Hi again, Michelle and thanks for your very helpful reply.
When you give him the medication, go in from the side of his mouth, where there is an opening between the upper and lower teeth. Squeeze in a little at a time, from the dropper, and wait for a swallow after each bit. You can encourage the swallow reflex by gently rubbing his throat.
It would be best to wrap him in a big towel, to disable all four paws and have just his head sticking out (like a 'kitty burrito'). If you have someone to help you, one of you can hold him upright, against your chest, and one of you can administer the medication.
I'm glad to hear his gums are a normal color and he's purring and playing; however, if he sounds congested and had an occasional cough and fever, he probably has an upper respiratory infection (kitty cold).
The medication probably tastes awful and that's why he's drooling. The swelling inside the mouth, under the tongue or on the jaw could have been caused from the dropper, when you tried to give him the medication or he might have banged himself on something and incurred an injury.
For the moment, I'd watch the swollen area and if it worsens or any of his symptoms worsen, it will be time for an ER vet visit. Monitor him throughout the night and call your vet in the morning, if there are no worsening of symptoms and he's still eating, drinking, eliminating and playing normally. I realize you said he wasn't drinking that much, so try to follow the medicine with a dropper full of water and a small meal or healthy kitten treat to help get the taste out of his mouth.
He's smacking his chops due to the bad taste in his mouth and this can also be a sign of nausea from the taste of the medication.
Put him in a room with a humidifier to help with his congestion/coughing and you can also run a hot shower to steam up the bathroom and then sit in there with him for 10 minutes a few times a day.
Cats rarely eat food with medication in it, because they can smell it, so don't put it in food again, but try the method I suggested.
I hope all will be well with your Boo and watch that swollen area. Please let me know how he's doing, tomorrow. Thanks!
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