I have mono and I don't know where I got it. I did some research and it says it takes 4-7 weeks to show up and that's not even full blown mono. I also read that even if it's been years you can still possibly infect someone else with mono since it stays in your system forever. About 7 years ago my friend had mono but I kissed her on Halloween this year, is it possible she gave it to me? I don't know where else I would have gotten it but it's so rare to infect someone that much later.