Welcome to Just Answer and thanks for your question. Thyroid hormone will not cause breast pain. It mimics the normal hormone excreted by your thyroid gland. If you are having breast pain you will need to see your doctor for an examination to determine what is causing the pain. It can be infection, prolactin hormone problem, etc.
I'm glad I could help. We have 16 inches of the stuff if anyone would like to have some :-)