Yes, Lyme does cause both low lymphocytes and low monocytes. They are both a type of white blood cell (WBC) and make up the majority of the lymphatic immune system. Lyme is known to lower the immune response.
www.wisegeek.com/what-is-the-difference-between-lymphocytes-and-monocytes.htm Have you had a recent set back of any kind? Stress levels gone up or anything of that nature? Have you been ill with anything other than Lyme - even if it's just another one of the tick-borne diseases ramping up? Any of these things would give the Lyme bacteria the upper hand again.
For more information on these things, this seems to be a pretty good article:
www.lymebook.com/lyme-disease-nk-natural-killer-cells