nipple discharge

What causes a nipple to have tiny drop of clear water non sticky discharge only when squeezing it. I prob making it worse by squeezing it to check. But not pregnant. And been tested at doctors for pregnancy for being on the pill and only two blue dyes came up with this tiny thin barley visable line that wasn't a pregnancy. I never had sex and know cum on pants can't cause that. So help please thank you. And all including pink dye all negitive and dollar store/tree also negitive. So what is it. And very very little