constipation

Hello everyone,
My Father has Parkinsons and I want to help him. I am trying to educate myself as his desiese takes many turns and there is so much to learn. His most current condition is constipation. He has been constipated now for nearly a week. He says he goes bits at a time and his stomach is hurting him greatly. He has been taking metamusil and drinking juice and eating fruit to no avail. Does anyone have any suggestions. I worry that he stops taking his medications when he gets like this cause he thinks they are the cause, but then he gets almost helpless. Would a bowel cleaner work? any certain kinds? Please, any suggestions would be helpful