Gastrointestinal problem. Medication!

My mother had 2 piles operation, but that problem started once again but now with worsen condition. Now even food without spices and maida generate problem, she had to go 3 times to the washroom to get fresh and whenever presuss comes, it come with burning sensation in anal area and along with in stomach with watery stool just like loose motions. She takes in her diet milk, chapati and Oats and only some vegetables, which also doesn't suits her, she don't understand what to eat, whatever she eats she generate pressure after 2-3hrs of meal and had to go to washroom and whenever stool passes it goes with lot of irritation, burning just like if she had eaten spices. She is in great trouble and need help, pls suggest some medication