Sounds a bit like prolactinoma. Why isn't your doctor taking you more seriously? A breast ultrasound 7 months ago is not a diagnosis.
I'd talk to an ob/gyn and ask for a referral to a specialist. I don't know what kind, maybe an endocrinologist. It is not usual to begin to (or continue to) produce breast milk in relation to birth unless the baby is nursing. I don't know why any doctor would shrug it off.
I had this myself! A little disconcerting. Any time you have nipple discharge, get it checked out. They will make sure you aren't pregnant. I had an MRI at that time of my pituitary gland which can have a very small, harmless cyst that is well known for causing this. I didn't have that. SO, it was blamed on my out of sync hormones. I was naturally producing too much estrogen.
By the way, does it come out on it's own or do you normally have to express it? Weird question but relevant.
Prolactemia and galactorrhea both cause nipple discharge unrelated to breast feeding. Things like birth control pills, underactive thyroid (hypothyroid--- which I also had at the time I had this) , etc. can be involved.
Mine righted itself without intervention. I was having some other issues eventually of very long cycles (periods every 3 to 4 months), etc due to the thyroid and was waiting to see an endocrinologist. It took so long to get in that by the time my appointment rolled around, things went back to normal and I haven't had a problem since!
But you should have a bit more information from your doctor to fully understand what is going on here. good luck