if you've had mono before you will always have it the rest of your life. it's a virus which means it lives in your cells forever and things like stress or other sicknesses that weaken your immune system can make it come up again, so take care of yourself
i have been taking something called monobrex and it has totally changed the way i feel (in a good way). i'm pretty much over mono now, and i was told i would have it for like a month or two before i even began to start really recovering. this stuff is supposed to help your immune system, i think, so you get over it faster than just lying around (even though you need to get plenty of rest, too).
anyway, since it's always in your system, you can pass it on to other people who haven't had it. the thing is, most people already have it, and when they're little kids it looks like a cold or fever, so most people miss it. when it acts up when you're a teenager or adult, that's when it knocks you down really hard. for most people, if they've already had it, they won't get sick if you kiss them. there's no way to know they've had it, i think, unless they tell you. i don't think tests will show it unless it's flared up.
anway, i hope you're getting better. and watch how much spit you swap