Have you talked to your doctor about it?
Just reading briefly, it's normal to have low prolactin levels (less than 25 ng/mL) for women who aren't pregnant. If you were trying to prepare to breastfeed and your levels remained low that might be something to talk to your doctor about. However, I wouldn't worry about it for normal breast growth.
The things you should focus on to promote good breath growth are things that keep you in good health generally, like
- eating a healthy and diverse diet (e.g. incorporate more salads with vegetables and nuts, choose less refined sources of carbs like whole wheat instead of white bread, etc.),
- staying hydrated (keep water by you all day and drink it regularly),
- avoiding drug use (especially tobacco and alcohol),
- keeping good sleep hygiene (helpful PDF),
- regularly exercising (both aerobic and strength training, aim for 1 - 2 hours of intense aerobic activity per week),
- reducing stress (including worrying about your prolactin levels, lol; meditation can help with stress reduction & helping to identify and redirect unhelpful thoughts; recommended reading: Judson Brewer's Unwinding Anxiety, and for a meditation manual, The Mind Illuminated by John Yates).