Can getting diagnosed with mono a second time point to another illness?

https://www.medicalnewstoday.com/articles/can-you-get-mono-twice#can-you-get-it-twice You don't get mono twice(highly, highly unlikely) but it re-activates in your body ( as it lies dormant in your body-as do all viruses of that class(type) - herpesvirus) . It does re-activate at times under stress including other disease conditions. Would follow up with MD

There is more than one germ known to cause a mono like illness. The traditional EB virus is most common. You do not indicate how the diagnosis was made in these cases. By itself, having the syndrome twice is not particularly worrisome.