I Having Trouble With My Stool From Past 4 Months

I am 64 years old. I had a operation of phistula 20 years ago. Now from past 4 months I having trouble with my stool. Sometimes I am not able to control my stool. The stool comes in the liquid form while passing the gas. It happens on almost alternate days. I am also having another problem. Mostly the stool comes out in thin liquid(watery) form. Because of that I have also lost my weight. The other problem is I do not find my meal tasty. I feel pain in my food pipe while taking in the food. Yesterday I had undergone the endoscopy. But the things were normal except that there was some swelling in outer part of my stomach. The doctor told me that it is normal and the results of the test are OK. Please advise. If you need any additional information, please let me know.