exactly what @ebv_fatigued said. mono essentially stays in your system forever. the symptoms will come and go as they please, and some, but not all, are effected by ebv (me being someone as well). i was diagnosed with mono about 6 years ago (i'm almost 20). whenever i am sick, i get the white tongue and my lymph node that was affected still swells. it attacks your immune system. im not sure if you have any other issues as well, but for mine i have been sick ever since i had mono. constant sickness. never really gets better. always tired, can sleep for 10 hours wake up and feel like i havent slept in over a week (i get an average of 7-9 hours a night). so it's pretty common and it will constantly show up
Blood tests will always show a past infection. EBV never leaves the body once you have mono.
white tongue is caused by many things and it could be from mono