Lactating but I'm not pregnant?!

Daisy • Just tracking my monthly days. Not TTC anytime soon.
I was pregnant a few weeks back and I had to terminate due to medical reasons. The abortion was about 3 weeks ago and 2 days ago my bf and I were just fooling around and he noticed I was lactating. 
I don't know if this is a normal thing. Anyone ever had this happen? Or does any one know if this is something to get checked out? Also I am on birth control, Depo shot, so I don't know if that has anything to do with it.