Suggest treatment for indigestion

my 10 year old son suffers with lack of control over bowels also has slight behavioural problems and we think it is due to mmr neadle. Has had no joy with medication for his bowels. He came in yesterday and had not made it to the toilet in time as often does, the smell is unbearable even when been to toilet seems to be in back passage constantly. Constantly at doctors get no joy. Very concerned as he has no control over when it happens he could be out playing or at school. Smell is very very strong when he has been to the toilet can smell the whole house upstairs and down.