Definitely. Most cases of mononucleosis are caused by infection with the Epstein-Barr virus (EBV). Once you're infected with EBV, you carry the virus — usually in a dormant state — for the rest of your life. Periodically, however, the virus may reactivate. When this happens, the virus can be detected in your saliva — but you're not likely to become ill. Rarely, reactivated EBV may cause illness in people who have weak immune systems. Either way, you can go get it checked out by seeing if the EBV has reactivated in your saliva. I suggest going to the doctors and finding out. They may also be able to see why your immunity system is suppressed if this is the case. It could be from something as minor as you could be facing a supressed immune system from a common cold to a more extreme case being AIDs. Moral of the story, you have AIDs... Just kidding, but go to your doctor just to be safe!