My Husband Has Constipation The Last 3 Weeks. He Goes

My husband has constipation the last 3 weeks. He goes to the bathroom about once a week due to taking oxycodone for pain due to a recent surgery. He is on dialysis so he doesn't drink a lot of liquids. He was advised by his doctor to take miralax which he did for 5 days . When nothing happened she stated to take a glycerin suppository and then a warm water enema. The glycerin suppository only made him pass 2 very small hard stools and so far the enema of water has done nothing. it has been almost 45 minutes. about 1/2 cup of warm water was used and when I tried inserting more water it would not stay in. Can he take another glycerin suppository to help??