My last blood test showed my white bloodcell count 2 points low. What causes that? I'm diabetic taking 1-500mg metformin per day

Maybe normal. Without seeing the numbers i cannot say whether or not that represents some illness or is just outside of the normal range and means nothing. If this is the first blood test to have this abnormality, it would be a good idea to repeat it to see if if might be an error. If a doctor ordered the test ask him/her for an explanation.