DR. called and I need more blood work. Have a low white count?

The title says it all. Last week I went to the doctor because I've been having some stomach issues the last 2 weeks. needless to say before I left I was scheduled for a sonogram of my gallbladder and had blood work done. They also put me on pepside for a month. To day the nurse called and said they want me back in for more blood work because my white blood cell count was low.Anybody else have this happen and what do you think it might be? I feel fine for the most part but can't eat out any more ( the food goes right through me) and certain foods bother me if I eat them. The pain I get is on the left side rather than the right like it should be if it was your gall bladder but we all know that not everybody is the same and gall stones can do funky things as far as symptoms go that is why the sono gram of my gall bladder was ordered. any input would be helpful.