I got these strange brown stains on my chest(collarbone area),started out a pink color,what is it?

We have not examined you, and most of us are not doctors, so we can only guess. My first guess is you are deficient in vitamin E and those are stretch marks, a form of scar tissue. It is cheap and safe to test. Get "Pure Vitamin E Skin Beauty Oil" at the cosmetics counter. Be sure it says "Pure". You can also use capsules by poking a hole with a pin and squeezing the oil out. Vitamin E has to soak in, so put it on when you can leave the skin bare for a while. That might take a week or two to show results.