Can you lactate but not be pregnant?

Apparently so, yes.

Yes... although pregnancy helps with boosting the hormones necessary for milk production. We had a nurse at one of the hospitals I work out of who prepared to breastfeed, in part, her adopted baby.

Yes you can, if you have a hormonal imbalance; specifically an over production of prolactin. I know this because when my cousin was 15 she was producing milk and had to go to the doctor. I am not sure what they did for her but it stopped.

I would get it checked out by a doctor if I were you, especially if you want to be have a baby some day.