Doctor is referring me to hematologist?

I had routine blood work done recently and got a call back from the doctors office saying I need to see a hematologist . It wasn't the doctor it was her assistant. She said the doctor was referring me because my count was 4.4 and back in Dec. it was 6. something . She also said they were referring me to study my blood because it has to do with my white blood count not red. So any ideas what this could mean. What could cause a problem like this ? Could it be cancer ? I know I don't have HIV . What other type of problems could cause this ? Could it be diet ? I haven't been eating the same because my cholesterol was high. Could it be just iron deficiency. I don't feel tired. I lost weight but than I put some back on. I lost weight because I was eating less. I 'm just worried about it .