Okay first off do NOT feel embarrassed or silly about going to the doctor for anything. GO. They will probably be able to give yo more insight than anyone here can. I've read that our hair skin and nails are a reflection of what's going on inside us so yes I would suggest you going to the doctor. Uhh..no stressed so the only thing that immediately comes to mind is perhaps medication. Also do you work out? I read the working out causes an increase of testostrone in women which causes us to have more of something call DHT which leads to thinning hair but I'm not sure how true that is. I always suggest vitamins but you're 15 so talk to your doctor about it. Perhaps they can also recommend someting topical as well.
Good luck Hon.