Hi My Son Is Suffering From A Very Sore Tummy

Hi my son is suffering from a very sore tummy and has been told his stomach lining is probably worn and that he has a lot of acid. I wanted to use milk of magnesia for him but can't get it. He is 24 and has recurrent bouts of very sore stomach. What foods would be good to line the stomach? Should I give him interflora as well? Hope you can help