I had this last cycle, and went to the doctors. She checked me & asked some questions 'does it leak by itself or when you squeeze' 'is it both or just one' 'have you been pregnant before'
She took blood to check certain things (hormone levels / thyroid etc) all came back normal.
Mine seemed to only leak when I squeezed it. So she wasn't super concerned but as it was one breast and I've a history of breast cancer in the family she wanted me to go to the breast clinic. However! I didn't fit the criteria..I'm going back next week, she said keep an eye out and if it's leaking on it's own she'll send me through.
It can be caused my stimulation though, she said.
Haven't checked since and it hasn't leaked by itself as of yet. Just my experience. Good luck! xx