Hi. What you are experiencing is pretty normal for puberty. Periods are sometimes irregular when you first get them in your early teens. I remember skipping my periods a few times when I first got it at 11 too.
Your body is changing because of puberty and the associated hormonal changes. More fat deposits, especially around the hips and breasts are common, and yes, it's normal to have big breasts once puberty hits at any age. Your body type is determined to a large extent by heredity - so you may be like your mom or like females from your dad's side of the family.
Don't worry about the changes as long as you are healthy and happy. If you don't get your period and that bothers you, speak to your mother or a trusted relative and visit a gynecologist to rule out any other concerns. :) :). Take care.