I would absolutely get seen by another doctor. This is not normal, not at all. Blessings to you.
Actually there isn't much you can do as long as this fluid is being produced then it needs to be drained by one method or another. This is an unusually long time for a drain to be left in place. I believe I would get a second opinion from another Breast Surgeon. Until the tissues (both surfaces of the void left by the removal of the breast) "stick" together then nature will attempt to fill this void with something which happens to be fluid. Speaking of my own personal experience, my initial drain was removed but some fluid did continue and rather than drain it with a needle my surgeon replaced the drain, which wasn't a big deal. under local anesthesia and it remained for another 10 days or so until the fluid production was minimal. I agree with your Radiation Oncologist about NOT hitting it with radiation; radiation is known for delaying healing !!!! I'd get another surgical opinion if at all possible. Regards..