Is there a treatment for alopecia nervosa, and how do I get my hair to grow?

Reduce stress. If you are experiencing a lot of stress and noticing hair loss, the treatment should focus on reducing stress. Make sure you are not pulling on your hair, which will make it worse. Healthy nutrition is also important for many reasons.
See dermatologist. There are many treatments that may require prescription medications or injections. However a dermatologist may first perform a history and physical to exclude the possibility of other causes such as endocrine disturbances.