Yes that is normal for some.
Never heard of it affecting havin kids. You can talk to your doctor though just to be sure it is normal for you. It shouldn't affect it but I am not a doctor. I know girls that start swimming before their first period will sometimes not have their first period until they are like 18 because it's an excessive amount of exercise. Again though, jut to be sure, talk to your doctor. It's always good to keep them in the loop anyway
As long as you are not at an unhealthy (underweight) then I would not be as concerned. I have a friend who works out everyday and she has the same issue.
That happened to me also. It is because your body fat has dropped below the normal level for girls. There isn't anything a doctor will do about it. Many female athletes are lean to the point that their period stops. If you stop exercising and your body fat percentage goes up your period will return. My doctor told me this, just because you don't have a period doesn't mean your aren't ovulating, so still use birth control, you could still get pregnant.
Don't worry, it's all good!
Periods can be unreliable at the best of times but maybe exercising is changing the body's rhythm and that's why (apart from pregnancy, fatigue and/or illness) your periods have stopped.