I think my horse has stomach ulcers...?

i have a 15 year old off the track Thoroughbred, he has been off for 4 years i have had him 1 year. the lady i got him from was treating him for stomach ulcers when i got him. he used to be on two scoops of grain a day, roughly 4 lbs, 12 pounds of alfalfa cubes and 14 pounds of good grass hay. HE WAS A HEALTHY WEIGHT. this spring he got an abscess in each front hoof, and lost a lot of weight. that was two months ago. we put him on 4 scoops of grain (DOUBLE), weight supplement, 1/4 pound of rice bran, 1 pound of beet pulp, 12 pounds of alfalfa, and all the grass hay he could possibly consume. two months later when he put on little weight but we are still struggling for a healthy weight. when i asked my mom about the possibility of stomach ulcers, she yelled at me for being paranoid and over thinking the situation, she refuses to even consider that there could be a problem. im scared because we are going on vacation for two weeks and she wants to cut his grain in half (which would destroy any weight i managed to put on him!!) and keep him out side for our whole vacation.