What Are The Likely Causes Of Low White Blood Cell?

What are the likely causes of a low white blood cell count (3.1)? I have been tested for mono, chronic fatigue, lyme, and several other things. I fainted and that is what kicked off the testing. In the ER, my white count was low, so they had me follow up with PCP, it was low a month later and again for the 3rd month. They are sending me to a hematologist for more testing, but I can't get in for a month. I know they did a smear with the last CBC. The nurse did not explain results. I will call to see if I can speak to my PCP about this further, but she is usually very vague and leaves it to the specialists. So my questions are why are they sending me to a hematologist/oncologist as opposed to immunologist or other speciality? What do you think they will look for next? All I can think is it has to be something serious...could it be something simple? I am seeing a neurologist...he thinks I may have vertigo by my eye reactions...getting a test for it later this month. My normal tests were ekg, eeg, ultrasound of carotid arteries. I have a few neurological symptoms, pain on right side near abdomin, diareaha with lots of gas and discomfort. I am 32 years old, female, who loves to run. I am in shape, excellent health when I just started feeling like I wasn't myself. I had fatigue, low grade fevers in evening, and like I couldn't run several days in a row. I am normal weight. I have 3 children.