I have seen on the net where people in Scandanavia are okay on their Vit. D levels even in the winter because they have a lot of fish, therefore fish oil with all its vitamin D. A daily tablespoon full of Norweigian (less likely to have mercury) cod liver oil might not hurt, therefore!
Whether or not parasites can cause you problems with Vit. D I do not know, but there are supplements and I guess you could get your levels checked again.
Dr. Mercola's site is big on Vitamin D info in case that helps.
I hope you are doing maintenance for the parasites. It's not just a one time deal.