I had mono my freshman year of college. I tested negative twice before I got a positive test. The swollen lymph nodes were HORRIBLE, I couldn't swallow even liquids without extreme pain; and, nothing helped because it was the swelling causing the pain, not throat irritation causing the pain. I don't remember about a fever to be honest, it's been 30 years. I slept constantly. I had no idea you could sleep so much. I was still going to classes (I know, I know) and I would literally fall asleep trying to write notes during lectures. I'd wake up and my handwriting would just have trailed away.
Mine only last a few weeks; but, I caught absolutely everything for the next two years and my glands would swell every time.
I've known people who were symptomatic for months and some who missed a semester of school. Praying he's on the tail end and there's nothing else going on.