Unfortunately, there isn't a lot you can do to speed up growth, despite what some unethical businesses will try to tell you.  Hair grows on average a half inch per month.  Some people grow hair faster, some slower, and some have hair that grows at different rates throughout the year.  In any case, you should expect a total growth of around 6" per year, less anything you cut off during trims.  It sounds like you are right on schedule!  Keep your hair in the best condition you can and it will grow at the fastest rate at which it's capable :)