The human immunodeficiency virus (HIV) causes impairment of the immune system by attacking a specific type of immune cell called the T helper cell. The cell represents a more minor fraction of your white blood cells. Thus, people with HIV actually don't have white blood cell counts that are really low. This is because the other cells are not effected. This is why we follow the T helper cell counts instead of the white blood cell count when measuring the severity of the HIV infection.
When someone contracts HIV, there are usually no symptoms for about a month. After that time a flu - like illness
develops where people feel sick, develop a sore throat
, enlarged lymph nodes, night sweats, and sometimes a rash. 2 months after this the HIV test become positive. If it has been more than a couple months since your encounter, and you never felt sick, then it is unlikely that you got HIV. It is still a good idea to get tested.
Other causes of a low white blood cell count include severe infections and leukemia. Keep in mind that a "normal" white blood cell count is very variable and normal can be anywhere between 3.5 thousand and 10 thousand. Being on the low end of the spectrum does not mean you have a problem.
I suggest that you schedule an appointment with your primary care physician
to get your HIV test back. The two of you can discuss measures you can take to prevent the contraction of HIV. Good luck.