GIRLS! Please answer, is this normal? ?

sounds normal to me, AFAIK women have varying cycles and even 21 days seems normal, 28 days is just the most common cycle length is all, also at 13 your body will take some years yet to settle down into it's "normal" cycle. You shouldn't run out of eggs and if you're concerned about when you'll go through the menopause your mum is normally the best guide, though there's no way to predict for sure, it's one of life's wonderful surprises :oP