What Causes Abdominal Cramps Along With Mucus Blood In Bowels?

My doctor put me on a Medrol Dose Pack three days ago for acute sinus pressure. That is better, but now I m having stomach cramps and bloody mucous in my stool. Otherwise I feel good. Can I stop this medication without side effects? It s Saturday night, we are leaving on vacation early Sunday morning, and I can t reach my doctor. I m frightened.