Mono is sometimes really hard to diagnose, and blood tests can be negative until the illness is pretty full-blown. When I had it I had low grade fevers and headache daily for about
6 weeks before the huge swollen glands and sore throat came on. That was when the blood test was finally conclusive. I was 16 and slept like the dead for 10 days.
My daughter had it at age 7 and at first her DR diagnosed strep (her fast culture was +). She didn't get better on antibiotics and kept on complaining about how tired she was, so we went back and she tested + for mono. Her tiredness was gone within a week.
I don't know about the lymphoid hyperplasia - I think it's an odd coincidence that you had a scope while sick with mono and I'd be shocked if there was a lot of data about that, but let us know what your GI says! Mono can knock you for a total loop, especially if you're an adult, and you might need to talk to your DR about liver function while taking your Crohn's meds and getting over this virus.