Dear mreeves, Breast pain is a common breast symptom. The reason for breast pain is not clearly understood, and is not usually associated with breast cancer. Breast pain is sometimes associated with hormonal variations and is then called cyclical breast pain. Noncyclical breast pain does not seem to be linked to hormonal variations and is often localized to one area of the breast tissue. Noncyclical breast pain may or may not be the result of an injury to the breast.
In terms of side effects of your birth control pill breast symptoms that may be associated with it include; breast tenderness, enlargement or nipple discharge, nothing mentioned about increased lumpiness.
It may be worthwhile to have yourself checked by a breast specialist, to be sure of what you are dealing with and perhaps some suggestions for easing the symptoms.
what you describe might be ectopic breast tissue; meaning, breast tissue located away from the breast. The underarm is a very common place to find it; when you get fibrocystic changes in the normal breast tissue, it can also occur in the ectopic tissue. It's not dangerous, but it can be more uncomfortable than the normally located tissue, and when it bothers a person enough, it can be removed fairly simply. Seeing a surgeon who does breast surgery would likely help to figure it out.