My super thick hair became fine

My hair was SO thick when I was in my teens and twenties, I couldn't get a scrunchie around it. But for 2yrs it's become so fine (not thin) that I can't keep the small clear elastics in it. I think it's related to hormones (possible endometriosis, my ovaries are discloured). So far I'm treating my hair with my own mix of thyme oil, castor oil, argon oil, and almond oil, I'm also keto so eating very healthy high protein foods and haven't coloured or bleached (yet). Any advice for thickening hair?