How To Cure Bruise Along The Spine Which Are Yellow Brown In Colour?

I'm 17 years old and I am very thin. Over the last 1.5 years I have developed strange bruises along my spine that are a yellow brown colour. I also have these strange scars horizontally across my back like I have been whipped or scratched, they look like stretch marks but feel like scars. I have not ever experienced any pain from any of these marks.