Do I have acne and if so how can I help it?

I am a 13-year-old boy and one day spots started showing up on my chest, these then spread nearly everywhere on my body bar my face, calves and pelvic region. They vary in size from very small to around half a centimetre, all red in colour and mainly concentrated around the chest. After being subjected to hot water they become blotchy and more prominent. Just before this, I noticed a blotchy mark on my leg wich was red in colour with skin flaking off occasionally. It is around 2.5cm in length by around 2cm in width. I was wondering what this was and if I need to do anything to it?