Hun, as Alty said...Don't put the cart before the horse. Let's find out if you are pregnant first. Get a HPT and use it when you first get up in the morning and pee.
The stress from thinking you are pregnant might be what is delaying your period. You are only 15, so most likely, your periods are not 100% regular yet and this may not even be considered late.
Alty is right. Raising a child is very hard work. Not only am I a mother of 4 children, but I also deliver babies for a living.