well, don't quote me on this, but I hear that when you shave you stimulate the glands make your hair grow so it makes it grow faster and stronger, however, if that were to be true than the people that suffer from baldness could just shave their head all the time and grow a full patch of hair. :)
It is a myth, what does happen however, is your hair grows back coarser and it only appears to be thicker, so the the ends are flat as opposed to a hair that hasn't been cut where the ends would be pointy
Your hair does grow back thicker. Since you're a girl, do not shave any facial hair, and don't shave the tiny hairs on your stomach. When I was a little girl, I shaved my upper lip hair, because I didn't know any better, plus I was going through puberty, and it did grow back thick. What's even worse, is that I'm naturally tan and I'm a brunette. So, now... everytime I see my upper lip hair growing back, I have to pluck it.
Myth. After you shave it seems to grow faster because you can see the length difference easier because it's nearer your skin. And it feels thicker because you have shaved of the thinner part of the hair (the ends) and you are feeling the thicker part (near the skin). Age can make it thicker, but not shaving.
Shaving your upper lip when a female does not make it grow back thicker. You may have to do it once a week or fortnight but waxing only gives longer time between waxing cos it lifts the hair out from under the skin. Shaving only cuts it off at surface level. Plucking is weekly as that seems to stimulate the follicles because you pull one hair out at a time from below the skin as opposed to waxing which is quicker & pulls out alot of hairs per 2 inch by 3inch sections at once.