Hair Thinning on Only One Side of Hairline

Hello, I am 21 F and my hair has always been pretty good, I shed a lot that’s about it. But I just realized that my hair is only thinning in one spot that’s on the side of my head. It’s the left side and I’ve never had this problem before. I wear my hair in a bun almost every day because my hair is curly and annoys me. I also use got2b glued: styling and spiking glue, to slick my hair back when I put it up. I understand this could possibly be tension breakage or something but I don’t really know why it’s one side. Any advice on how I should proceed would be greatly appreciated.