Could my prolactin secreting tumor which is causing elevated prolactin levels also be affecting my thyroid?

Possible: If your prolactinoma is enlarging in size, then it can potentially create a pressure effect on cells in the pituitary gland that secrete tsh, the very signal that controls thyroid gland hormone production. I urge you discuss this with your endocrinologist to see if imaging study is needed.

Prolactin: A tumor of the pituitary can interfere with other pituitary hormones like tsh. This hormone stimulates thyroid hormone secretion and if low, can cause hypothyroidism.