I used Grape Seed Oil with my DE mix. This may be why you have trouble spraying it. It doesn't really spray, it squirts with the spray valve wide open. Grape seed oil is important because it soaks into the skin rapidly.
The only things I used were low sulfur cream (like a jar of vaseline) & low sulfur soap when I took a shower (3 times a week ).
All itching was gone within 2 weeks. I kept it up for 2 months to kill the babies as they hatched under the skin.