Doesn't chemotherapy mess with blood chemistry and cell counts? I would think that what you are experiencing has a lot to do with going through chemotherapy. There are several ways to bring up cell counts.
One is by eating foods with iron in them. Which include liver, green veggies (especially fresh spinach), black strap molassis.
There is something called procrit and there are also iron tablets.
I think this has more to do with having had chemo and radiation than it does with having thyroid removed.
Thymoma is cancer of the thymus, which is totally unrelated to the thyroid, except that it controls immune processes.
Why did you have your thyroid removed?