Does walking for a few hours straight make pneumonia worse if one's having difficulty breathing?

Rest and hydration: If you have pneumonia, please rest, drink fluids, and follow up with your physician for shortness of breath.

Some basics: The work of healing requires that the body shift resources from muscular & thinking activities to do the work. If you are busy trying to walk or do regular work activities, you do neither those or healing well. Shortness of breath means your lung function is poor enough to tell you you need to slow down. Rest, hydrate & nourish yourself so you can heal. Otherwise you can make it worse.