Also, they say that you should call your doc if you feel more than 4-5 an hour (unless you are in late pregnancy, then you get them all the time) but I'd try laying down and drinking a lot of water first. They usually are triggered by dehydration and/or overexertion.
No! You actually can start getting them as early as 6 weeks, but you don't feel them until your uterus is big enough. It just depends on your body and sensitivity. I always felt BH pretty early.