Gagging could be because of acidity or heart burn due to reflux disease .
YOu took antibiotics that could have irritated your stomach and throat so you need to take --- Antacid
Syp. antacid gel 2 tsf two times a day half an hour before mealsmultivitamin
Keep head end of bed elevated.
Avoid alcohol, Smoking
Do brisk walking daily
Go for walk after dinner
Avoid spicy food
Avoid late night coffee
follow up after 7 days.
Also take care of runny nose as that could be the source of recurrent throat infections for that you can take antihistaminic tablets easily available.