What's going on?? Clear liquid coming out of nipple.

C.
So I am 2 weeks late for AF, all BFNs so far. My dr put me on progesterone for a week to restart my cycle since my tests are all negative. (My cycle is extremely regular; I can't remember ever missing a period).
Today I was standing in my night shirt and a drop of clear liquid came out of my left boob and soaked my shirt. I can't find anything online about this being a side effect of the progesterone- all I see is that it's a pregnancy symptom. I'm going crazy thinking that there's still a chance that I could be pregnant. Please keep me from going crazy! What is happening??