My sister had a real problem with this a while back. Finally she had to go to the emergency room the pain from constipation was so bad.
They gave her a recipe for what they call a “Brown Bomb”.
1 cup of warm Vernor’s, not sugar free, warm it up a bit in the microwave.
1 cup of prune juice, (you can warm this up with the Vernor’s if you want to.)
1–2 ounces of Milk of magnesia.
Don’t drink this all at once, but have about half of it then the rest a few hours later to keep things moving.
It takes about an hour before you will get results, but stick close to a bathroom for about 6–8 hours.
You will have more than one trip to the bathroom.
You might also want to get some glycerin suppositories to help things be more comfortable at first.
After the initial “clog” is gone, then following the advice of fiber and water and other non-constipating foods is recommended.