You don’t go HYPERthyroid after RAI, but HYPOthyroid. RAI destroys the thyroid, so that it cannot produce thyroid hormone any more.
As to why you might still be experiencing hyper symptoms, you need to ask your doctor. I assume that you are having blood work done regularly. The docs might have given you a smaller dose than you need? Some people have to have RAI twice. Anyway, your doctor is the one who would be able to tell you.