Originally Posted by Cogito Ergo Sum

Painkiller should never be taken for a long time without doctors' advice.

But as the problem has already been created, I suggest you get yourself a prescription of Antacids and/or PPIs for ulcer/stomach issue. If you don't want to take any further medicine, just do these:-
-Avoid cola, tea, fried food, spicy food and cigarette for one week
-Sleep with double-pillow (to keep the head raised)
-Eat light and make sure to not have anything to eat at least 2 hours before bedtime

Your problem will hopefull be solved in a few days inshaAllah. If it persists, go to a doctor to get a proper prescription.