He has（persistent）constipation / irregularity.（他经常便秘。)
He has been unusually constipated.（便秘很反常。）
He is having problem with irregularity / constipation. （他便秘。）
He has no bowel movement for the past few days. （过去几天他都没大便。）
像这种肠胃毛病除了要听取医生的意见，还要多从饮食上找原因，健康饮食、多吃青菜，得病的可能性就小很多啦！