Breast is meant to produce milk and especially in ladies the breast serves as a organ to produce milk for the baby's growth and nourishment. Once a person has pregnancy the breasts undergo lot of changes and it causes them to produce milk.
But every secretion from nipple is NOT milk. Such secretions are also produced by other hormones like
prolactin,
thyroid hormones, etc.
Since you say that you are fatty, the excess weight gain could be hormone induced and hence it would be better to seek help of a doctor and get examined.
The doctor will examine for any lumps etc and also ask you to go for hormone tests. Sono Mammography may also be advised.. So meet a doctor ASAP