When someone has trouble with making bowel movements (pooping), they are "constipated". When you're constipated, you don't poop as often as usual.

"Constipated" is an adjective:

He's constipated.

The noun form of "constipated" is "constipation":

One of the side effects of the medicine she takes is constipation.

We use this word when talking to a doctor or nurse, and also when talking about this condition in regular conversation.