Yeah man, it's normal. You're a late bloomer, and you'll definately grow! It just takes some time with people who are late bloomers, but you definately sound like you're in puberty, so it's all gonna come soon (probably see growth before next year)! =]
As far as girth, I wrote the "Puberty FAQ and Information - THIS MIGHT ANSWER YOUR QUESTION
", which answers what it is. Girth is the circumference or distance around the penis.
You can find out how to properly measure girth Here, in the *** Ask ALL Penis Size Questions HERE *** thread
Don't feel like you're the only late bloomer...There's plenty of people around the site who can relate to you, and they've started developing after 14 and 15 and are doing just fine now! =]