Hi Marie:
A Hemotologist is a blood disorder specialist which includes a wide range of blood diseases, of which some belong in the cancer group. For example, most anemias have nothing to do with cancer, nor does thalassemia.
Some meds can suppress the bone marrow which means they suppress blood component production. This in turn means fewer white blood cells being produced, thus a suppressed immune function.
Mono, a virus, can also affect the immune system function.
Basically, you've got three possible and different reasons for your reduced immune function. So, unless there's a very specific test or series of tests that your doctor[s] can do to obtain a specific diagnosis, they're going to have to treat you symptomatically. There's also a possibility that each of the three factors are actively contributing to your current health status, thereby requiring a three-prong treatment.
All of these are merely guesses. Do try to get as much information from your doctors as possible. Also, please try to not get discouraged if you don't get a firm diagnosis right away.
Suggest you look up more information on the MedLinePlus database - it's part of the NIH so the information is quite reliable. MedLinePlus has both medical and drug information.
[url="http://www.nlm.nih.gov/medlineplus/healthtopics.html"]http://www.nlm.nih.gov/medlineplus/healthtopics.html[/url]
Good luck,
Jay
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Very scared, need some advice 
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