The link doesn't work, but it sounds like ingrown hairs. They can be caused by friction from clothes, shaving, or heredity, especially if you have curly or kinky hair. Lotion or powder will make it worse. When you shower, exfoliate the areas gently with a washcloth or loofah.
Oh, and fifteen is too young to be having sex. Do yourself and your gf a favor and wait. :-/