Hello and welcome to EmpowHer,
I suggest that you have your hormones tested to see if there is any imbalances. It is common to have headaches and even migraines from hormonal imbalances. The removal of the thyroid often helps to balances the hormones but this is not always the case.
If it is not a hormonal problem than it may be caused by any number of things such as:
The list could go on; but these are common causes. Common testing for causes of migraines include: MRI, CT scan, and blood tests.