This is a problem I've had to deal with for far to long.
I even visited an ER one night. Meet a nice Dr. who after touching my abdomen and I nearly jumped off the table! He told me to me to just walk of the ER without talking to anyone to save myself some money and go to the nearest all night drug store and buy a few bottles of Magnesium Citrate.
Drink the entire bottle. Don't worry their small and stay close to a bathroom.

Wow was he right. Worked like a liquid rotor rooter.
Now I use Metamucil. I haven't had to use Magnesium Citrate in a long time.
But I do keep a bottle of the cherry flavored Magnesium Citrate in the refrigerator just in case.
Best to be prepared.