Hi There, I Have Been Lactating In My Left Breast

Hi there, I have been lactating in my left breast for about 4 months now, I am an 18 year old healthy female who is on no medications and have no other health problems. I had blood work done to check prolactin levels, and also an ultrasound on my breast. Everything came back normal, my doctor is referring me to an endocrinologist to further investigate the cause of this issue... Was hoping you could shed some light on what's going on?