My white blood cell count is dropping

Hi guys, I have been on Aza/Imuran for 7-8 mos. My white blood cell count(wbc) has been low for a couple of years. It ranges from 3.4 to 4.0. It has been dropping a little lower slowly but surely. It was 3.4 for 2 mos. and it was taken again a couple days ago and it dropped to 3.2. I'm getting a little nervous. My doc is going to take it again in a month and I see him in Dec. Could it be my Aza that is doing this even after 8mos with no problems? Has anyone else has this problem and has been able to stay on Aza. I have been feeling well since I've been taking it and I don't want to stop.