What Causes Breasts Soreness With Discharge, Backaches And Nausea?

Thursday I noticed that my breasts were sore. Friday there was a white then clear discharge from them when squeezed. Sometimes there is a feeling that something is coming out of my breast but when i check its nothing. My last period was Sept. 6 even though it was 3 days late. I took a pregnancy test then and yesterday and both were negative. I have also had back aches and nausea. Could I be pregnant even though the test are negative?