Talk to General Physician on Weak Immunity System

My white cell count is between 2200 to 3000...n i have found about it in 2013 when i go for a blood then they have increased n decreased never crossed the 4k I have this condition called leukopenia, i have consulted so many doctors but couldn't find the cause of it ,one of the doctor suggested that i should take a therapy, because i take so much tension, even gone for a bone marrow biopsy but still all in vain. Can anyone please guide me about it..i don't know what to do about it cx i'm sick most of the time sore throat ,cough, stomach pain etc.