Can Omega 3 DHA Vitamins Cause Sticky Stools And Diarrhea In A Child?

My son often has sticky stools that are difficult especially at school. If not sticky then it s often Diarrhea. I began giving him Miralax as suggested by his pediatrician but I feel it made his problem worse at school. He is 9 and often the clean up requires a shower. He drinks a lot of water, I have cut down on greasy, surgery foods and it continues. Could it be the Omega 3 DHA Vitamins I have been giving him?