Google "too much prolactin" or "high prolactin". That is a hormone that, when too high, causes milk-like discharge from the breasts.
Also, there are three forms of estrogen that occur naturally in the female body (naturally, not put there by synthetic drugs) - they are estradiole, estriol, and estrone. One of them, I forget which, if it is too high, will automatically give the woman tender painful breasts. (not that this is the only possible cause of painful breasts, it isn't, but if you are high in that one type of estrogen, you'll have painful breasts.)
There are some internet sites that will do saliva tests for your hormone levels without needing to find a doc who isn't under the thumb of insurance companies. The site I've heard a lot of good things about is
but there are others - some with good reputations, and some with not so good reputations.