S.K.
Increased levels of the hormone prolactin can cause milk production in the breasts. Prolactin can be elevated in people with hypothyroidism, people taking certain medications, or with a benign (non-cancerous) tumor of the pituitary gland in the brain. There are a few other reasons for increased prolactin and sometimes the reason for increased levels cannot be identified (called idiopathic). I would double check with a pregnancy test and visit your doctor to get some testing done. It is probably not a serious problem, but it should be looked into.