Thanks for your query.
Take it easy, nothing to worry about. It is possible that your tissue is not completely healed inside. It may take more time to be fine. Other possibility is any infection have caused such discomfort, to exclude it you may need to perform test like CBC and ESR
. Then it can be treated by oral or topical antibiotics.
Make sure you are not a diabetic and having no kidney/Cardiac disease or any other problem.
I advise you to keep your foot neat and clean and take Vitamin supplements (specially vit B12).
Hope it Helps.
Take a Good Care!