Stretch marks I think?

So over the past year I've noticed some like red vein like things over my side. I think they're stretch marks but I'm not sure. Over the past few months I've noticed them more and more around my boobs. I'm nineteen and way past puberty. I'm wondering if I'm just getting fat (I've never been pregnant and I know I'm not) or if I should be worried or something. Has this happened to anyone else?