What Causes Spotting Along With White Liquid Discharge From Breasts?

Last Week I Was Spotting Its Started On Sunday. And Ended On Thursday. Now Today As I Was In The Shower I Dont Know What Came Across My Mind To Squeeze My Boob, But When I Did White Liquid Came Out. Now 2 Days Ago I Took A Pregnancy Test And It Said Not Pregnant. Why Is This Happening?