Is it normal that I’m lactating even though I haven’t given birth and I’m not pregnant?

I’m 26 years old. I was pregnant when I was 13 years old and I had a miscarriage. I have never been pregnant since, however, every once in a while, my breasts lactate when I get my period or under certain birth control. I have not been on any birth control in over a year and I am not on my period. I also haven’t been sexually active for a while, so I know that pregnancy is not a possibility. So, is it normal that my breast lactate still? I really hope its not cancer or anything of the sort.