Crohns disease and stomach pain

Hi there my partner was ill 3 years ago, he lost weight had constant diarrhoea and sickness and got the eretherma rash all on his legs. It took 6 months for the doctors to advise he had crohns disease. They put him on steroids then weaned him off them and put him on pentasa and he has been fine on that for 3 years until now. He has been getting really bad stomach ache at first it was after food then drink and now it can come anytime. Can anybody help or give any suggestions???