I noticed that you just joined the 21st of this month so you may not know how "complete" this web site is. As you will soon find, there are a number of sources you can go to for the help you're looking for starting with the "author" of this web site, Steven Ellis, (go specifically to his articles) as well as by profitting from the feedback that you will get from coaches and players via this forum.
I don't know how old you are, but if you've been pitching for awhile, you hopefully are aware that there's a lot more to pitching than simply using your back and legs when trying to gain greater velocity. If you haven't gone this route before, having someone videotape you throwing from the mound would be an important "tool" in your learning process. The naked eye often cannot pick up that which the camera can, particularly when something is done quickly. What you think you're doing may be inaccurate. Your mind can (and will) deceive you, but the camera won't lie. Your particular mechanics, broken down frame by frame, should give you all the information you'll need and the direction in which to go. At this point you might want to hook up with someone in your area that is knowlegeable referent to pitching mechanics and have him look at the tape and offer his suggestions. Later, if you're still confused you can always come back to this forum.
Additionally, Tom House's latest book "The Art & Science of Pitching" (NationalPitching.com) gives you a detailed breakdown of what you need to do and the drills to practice the specific mechanics.