Aromasin causes a pretty drastic chemical menopause - one of the symptoms of menopause can be headaches, sometimes pretty severe.
There are many message threads on the breast cancer message board about aromasin, arimidex, tamoxifen and the other anti-estrogen drugs. If you have some time, I think would be well-worth it to look back through the past messages - you have to sift through to find it, but there is lots of information about alternatives, and comments by ladies on what they did to lessen side effects.
(If caffeine doesn't make your breasts hurt, try Excedrin headache formula - has aspirin, acetaminophen and caffeine. Even though it's formulated for menstrual pain, Midol can also be very effective for headaches.)
Sincerely,
Tre