Why white cell count keep dropping?

If it is due to parasite induced anemia such as with hookworms, the RBC count would normally drop too.

The important question is which WBCs are dropping? T-cells? Which one?

Bone marrow biopsy can provide some clues but carries risks.

There are cases where the WBCs will accumulate at a site, making the blood counts temporarily lower.

Look for abnormal liver, spleen, thymus activity / sensitivity, or unusual swelling / tenderness in other areas of the body.

Also note that Ivermectin may cause low white blood cell count in 3% of people.