Shots in Head to Regrow Hair?

A couple of years ago, I noticed a bald spot in my head and got shots for the hair to grow back. I just got another one, but not as big. What is the cause of this? Can I prevent it from happening again?

What kind of shot did you get? Did your hair grow back after you got a shot a few years ago? I would hope a doctor gave you this shot. You should ask him/her these questions and ask him/her what they were treating so that you have a working diagnosis. Doctors have the obligation to educate their patients and communicate with them so that they are able to understand that is going on with their bodies. I would strongly suggest that you go back to your doctor and ask what was he/she was treating. I cannot diagnose your condition or even give you advise on your treatment since I do not have the advantage of examining you in person.