Try using Re-Gro.
Never let your hair get too dry. That could cause it to break and get thinner. Olive Oil and Pink Oil works good.. Also, you can try keeping your hair in braids. That makes your hair longer and thicker (you couldn't possibly damage your hair that way). But if you don't want it to be long, you can always cut it.
& black men's hair grows quicker probably because they don't do as much with their hair as girls. We straighten / curl / brush it all the time, and they don't..