I Am Constipated So Bad That The Stool Feels Like

I am constipated so bad that the stool feels like rocks and is very hard to pass. I had to stop my last bm because it was impossible to pass the stool and I became tired with the effort. Please help. I am taking lactulose which helps sometimes but not this time. Will Bisacodyl Suppositories 10mg work? I m a cancer patient and am on morphine 30mg ER every 8 hoursand 15 mg fast acting every three hours for pain.