hair growth, help!

When I was 16 (now 29) I cut my hair to about my shoulder blades. It hasn't grown since! I have tried trimming to get it to re grow, I have taken hair,skin,& nails vitamins, and now use a shampoo and conditioner with b7 & biotin and all the other good stuff to help prompt hair growth and still nothing 😩 it's even begun to thin over that last year. Does anyone know of anything that WILL make my hair grow again? I don't color my hair and I straighten it maybe 5x a year. I would really like my length back so any advice is greatly appreciated, TIA.