Stretch marks on boobs

I recently noticed lots of little purple stretch marks appearing on my boobs. I have already gone through puberty and didn’t get any stretch marks while my boobs were growing and my boobs haven’t grown at all recently. So I’m unsure why have have gotten them. I started using bio oil everyday but more still keep appearing. Everyone I see keeps saying they don’t go away and I’m really upset. I’m not sure what to do and how to stop them.