in my right breast. I have had all the usual mammograms and even some emergency ones in between. The last time I saw the breast doctor he was quite rude and asked me what medication I was taking, when I said Thyroxine (for the last 20 years) he said "Well, that explains it!" Does anyone else been told that Thyroxine can have this side effect. I do try to take Evening Primrose oil as that does eventually ease it. Should I be worried, I know that there are other types of breast cancer which do not show on a mammogram.