What Is The Black Liquid Coming Out Of Both Breasts?

I have black liquid expressing from both breasts on its own, which made me sqeeze to see if it would make more, and yes it did a lot. They are also very tender. I am 36 years old has a hyste when I was 26. Healthy otherwise. No meds, 5' 5" 140 lbs. I have 3 children oldest 18 youngest 14. I did breast feed all of them. I am scared because when I first had my surgery I did take hormone replacement, but stopped after reading it can cause breast cancer. I now take all natural suppliments approved by my doctor. Is this just a part of menapause or should I be worried?