You have a handle on the basics about right, I just say it a little differently.
IgM is usually taken to indicate response to antigens by the innate arm of the immune system. The shock troops of the immune system which can be rather non-discriminate and therefore rather harsh and ramps down rather quickly so as not to do too much damage.
In a properly working immune system the IgM response is replaced by the more targeted and less destructive adaptive arm, the IgG response. Sometimes called the memory part of the system it supposedly is responsible for rapid response to pathogens that the system has seen before -- for example to vaccination or a disease that you have "got over" so if it comes around again your system responds quickly because it already has the "template" of that germ.
If you catch the implication it means that a WB for IgG is only of value if done before abx is started. Once you are exposed to a bacterium or virus and get over it the IgG response, although it is still there, is in more of a lurking mode and causes no symptoms. It cannot prove current infection nor can the absence of IgG prove cure because some people ramp down to a level that may be below the detection level. Igenex has a graphic illustration of the process:http://www.igenex.com/timea.htm
EBV, Epstein Barr Virus, (mononucleosis) is just that, a virus, so abx will have no effect on it. Your immune system will suppress the symptoms (disease) but current thinking is that people will carry it for life with apparently little or no ill effects as long as the immune system remains competent.
That was a very oversimplified explanation. Wikipedia has a page on EBV:http://en.wikipedia.org/wiki/Epstein_Barr_virus
And the workings of the very complicated immune system fills volumes.
And you need to be able to make the distinction between chronic infection vs chronic disease. That, by the way, is the issue that is at the root of the Lyme Wars and is an issue that is not about to go away anytime soon.