Why are my testicles so itchy?
Anywhere new hairs grow is itchy. When you get older and shave, if you let your beard grow back in, it will be itchy for a while. Since you have pubic hair forming, it is itchy. Unfortunately all the pubic hairs don't develop at once, so the itchiness is dragged out a bit.
If you see red spots on your skin in the groin area that are itchy, it is a good chance that you got jock itch -- a fungus that gets into your skin. See Will jock itch go away on its own? for more details.