Is it normal for women not pregnant to lactate? Does it mean something more if it's only in one breast and not bilateral?

No. Lactation without pregnancy is an indication of some hormonal disturbance. You should visit your doctor and let him examine you and order tests to make sure your pituitory gland(located under the brain) is healthy. Sometimes a small adenoma(prolactinoma) in the pituitory gland can cause lactation like you have . It may require blood tests and x-rays of this gland to check you for this condition.