Your hot spot sounds too cool. Ideally it should be 88-92 unless you have an ambient of ~85, which doesn't require a hot spot.
Just because the heating pad doesn't feel hot to you, doesn't mean it's not too hot for the snake.
Humans are around 97 degrees. If it's warm to you, the pad is probably around your temp or higher.
Heat pads can get up to 120 degrees unregulated, which will definitely burn a snake. A Thermostat is a must have when dealing with heating elements in a reptile enclosure.
It should have been the first piece of equipment to buy before getting a snake. Without a thermostat, I wouldn't feel comfortable using a heat mat at all.
Also, intramuscular administration of antibiotics is more effective than oral. Snakes have a very slow metabolism, which is why oral isn't used very often in reptile medicine. Administering directly into the body is much faster in regard to the effectiveness of the medication.
From your description about your snake adjusting his jaw. Is he really adjusting or jaw or is he opening and closing it? There is a slight difference. If he's opening and closing it, it could be that he has RI, which is why you're hearing the clicking noise. Snakes who have RI, open and close their mouths to breath more easily. My snakes adjust their jaws after a meal, and I have never heard them click. I have also fed large prey once in a blue moon with no problems. (due to my stock of feeders getting bigger than their usual meals.)
Does he look upward often? Can you check his mouth if it's full of mucous? You can gently pry open his mouth with a q-tip to see.