My Son Is 27years Old He Was Diagnosed With Mononucleosis

My son is 27years old he was diagnosed with Mononucleosis a few months ago and he still feels extremely tired and he has muscle aches. These symptoms seem to come and go but he feels tired and exhausted most of the time. He has been quite healthy all his life except for this and he is in excellent physical shape. Could he still have mono after several months? He has a cat and a rabbit that hops around his apartment. Does rabbit feces on the carpet cause any of these symptoms? He does not have a very good diet. He is going to try a multi-vitamin but we do not know what else to do. thanks