I’m lactating but not pregnant

The other day i pinched my nipple and some milky white substance shot at my eye and ever since then, tiny little drops will come out of it when i pinch it, and occasionally a STREAM of it comes out. instantly i took a pregnancy test and it was very negative and the rest have been negative. it also started while i was on my period but has continued since it’s stopped. i have never been pregnant and i am on birth control and take all of the precautions to not get pregnant. i’m so freaked out why is that happening? please help