Hi, I don't think you have anything to worry about. Your WBC are within normal both times, it may look like it dropped because when you had your CBC the first time you said you were not feeling well - and probably had an infection (which was too mild to cause fever- infections can cause the WBC to rise). Tell all your fears to your physician on your next visit.
But then again we are either cancer patients or caregivers of persons with cancer here - we have a different "normal". If the values you posted were that of my husband's CBC- I would be jumping for joy.