There are so many infections that in many cases just give some abdominal problems and fatigue ++
Let us look at just an example
Trichinellosis is normally connected to severe muscle pain, strong fever etc.
But lets assume you just have chronic gastro problems, some weak muscle pain, chronic fatigue, should you then also be tested for this?
Most medical doctors would shake their head if you asked to be tested for Trichinellosis. Still if they were reading more books and listen to CDC they would see that Trichinellosis is one of many diseases that should be tested for in people with such symptoms that could be many many things.@
"Often, mild cases of trichinellosis are never specifically diagnosed and are assumed to be the flu or other common illnesses."
http://www.cdc.gov/ncidod/dpd/parasites/trichinosis/factsht_trichinosis.htm#s...
"Am I at risk for trichinellosis?
If you eat raw or undercooked meats, particularly bear, pork, wild feline (such as a cougar), fox, dog, wolf, horse, seal, or walrus, you are at risk for trichinellosis."
Very many people have at some point been eating undercooked meat. Dose this mean you likely are infected with trichinellosis. No most likely you do not have it. But for people having unexplained chronic symptoms, fatigue etc. This is possibly one of many infection diseases that should be tested for.
There exist simple serology tests for this. If you feel healthy please do not waist time and worries you could be infected. But if chronically ill for long time without finding out, then this is one of several diseases that should be excluded by testing!
But this was just an example, if reading the medical litterature in detail it should come as little surprise that many types of chronic infections can give similar and overlapping and non-specific symptoms.
The first step (and second step) should in my view be to meed a good infection specialist and get extensively tested out for possible diseases. If you have studied these things yourself it makes it much easier to discuss and come with suggestions to such doctors.
However do not think, or be sure you have this or that infection. This is a big mistake many do. There are so many types of infections that can give similar symptoms.