I was on a bio-identical form of estrogen (the patch) until recently when they found some breast masses. I had a total hysterectomy at 43.
I used to have a lots of breast tenderness even on birth control... So I would work with your doc both on form and dose to use the least amount and the most most bio-identical you can to reduce risk and side effects.
The tenderness could very well be a result of the change in the hormone levels in your body. Keep in mind that HRT has been proven to increase the chance of Breast Cancer. If absolutely necessary these drugs should be used at the lowest dose possible and for the shortest time possible. Regards .....