I just tested positive for Mono...?!

I just tested positive for Mono...?

and I've been reading a bunch of medical stuff about it, and I found that 95% of Americans get Mono at some point and then you always have it and cant get infectious mono again. if this is so, why don't they just give everyone mono when theyre little and then they don't have to deal with it when theyre older?
I guess they dont think its important enough since people rarely die, but it can make things very tough on people lifewise because of fatigue and conmtagiousness.

1 week ago
the 95% is from a medical website that says that 50% of people get it when they are very young, but it is a lot less devastating.

whats mono?