I just came across this online and thought I would reply. I am 33 years old and I had a pretty bad case of mono when I was 17 years old. I was out of school for 3 months. Lost about 8 pounds, and continued to "re-lapse" back into mono for the next 8 months or so. (Every time I would expend too much physical energy). When I had mono, I slept about 20 hours a day, I hardly ate anything (normal for people with mono), developed an incredible thirst for orange juice (and oranges), that lasted for about 4-5? years after the mono. While having mono, I also developed an enlarged spleen, hepatitis, anemia, jaundice, respiratory infection, bronchitis, and well, I generally felt like death for a while. I did get better eventually.
But my reason for responding is this: I don't care what doctors say, I am certain that there is a connection between mono- and post, unexplained medical problems. Honestly, I feel like I have had a 'weak' immune system since mono. I developed allergies out of nowhere. I have had a whole range of small, non-serious, yet very annoying and unexplained medical problems since I had mono. I don't think my body ever REALLY recovered. What would a doctor say? Probably that it's all in my head.
But doctors don't know everything.
I would say that mono, which severely attacks your immune system can absolutely cause lasting damage and weaken your immunity over the long term. For most preople? Probably not. Most people who get mono only have it for two or three weeks and then get better. I'm just saying, it's definitely possible.
Like I said, I'm 33 now. I have way too many stupid little medical problems for someone my age & health. I am physically fit. I eat very well. I do not smoke, rarely drink, and do not drugs. No diseases. I could probably stand to exercise a bit more, but otherwise I SHOULD be in very good health. But I'm sick constantly. Allergies. Sinus problems. Infections. Easily exhausted. Extreme sensitivity to cold weather. Get sick easily. Stay sick for 6-8 weeks at a time with something as simple as a head cold.