@anitapw, my son had mononucleosis but he does not have Crohns. it took him about 2 weeks before the fever and sore throat got better and about 3 months before he was able to go back to normal activities. My son was 22 when he got the mononucleosis. Though he felt normal after 2 weeks and can do normal stuff, the doctor still advised him to avoid strenous activities and contact sports. I think it is to avoid raptured spleen. He was not given any antibiotics,because the sore throat was not due to strep, they let the fever ran its course.