Hello. I Have Been Diagnosed With Breast Cancer (Stage 1).

Hello.
I have been diagnosed with Breast cancer (Stage 1). The surgeon who did my lumpectomy retired a few weeks after my operation. However, before she left, she set me up to receive radiation. The new doctor also prescribed a daily pill of Letrozole (2.5. mg) - 1 pill daily. During the time I was getting daily radiation, the new doctor was away. However, I took 1 Letrozole pill each day for about 2 weeks - but I had problems with my left eyelid drooping to the point I could not see well enough to read out of that eye. I told the radiology nurse my problem. She relayed my problem to the radiology oncologist and I was prescribed another pill (Anastrozole) and I had the same reaction. My question is: why do I have to take this pill as well as having radiation. ? How will it help me. Do other people have reaction to these pills?
My e-mail address is: YYYY@YYYY