help! i can't fix my hair

for about two years, i obsessively straightened my hair nearly every single day on high heat (400 degrees fahrenheit without any sort of heat protectant) until i realized that it was only getting frizzier and frizzier instead of smoother with each pass of the straightener and stopped. it's been a year and a half since then and i've only straightened my hair a few times since. however, my hair is still damaged and dry and i can't seem to fix it. i've tried a few different hydrating masks, leave in conditioner, repairing shampoo, coconut oil, and olive oil, but nothing seems to help. i've even tried olaplex no. 3 (exactly the way you're supposed to use it, as a pre shampoo treatment and not a conditioner, left in the hair for two hours or even overnight) but it seemed to do minimal good. i'm still in highschool, so i can't go ham buying different products or getting a professional treatment. how can i fix my hair?

for reference, i'm chinese, so i have thick, rather coarse asian hair. prior to the damage, it was long and very straight (i straightened my hair to get rid of the kinks left in my hair from tying it up) and hadn't been colored before, i.e. it was still virgin hair. now it's very frizzy and poofy, with weird waves in it. although my hair is still generally straight after airdrying and has no defineable curl, many of my individual strands are curled wildly and results in an overall mess of frizz. i considered that my hair could have become naturally curly due to hormones and i just wasn't treating it right but the bottom layer of my hair that i couldn't reach with the straightener is still stick straight and soft to the touch after airdrying, so i don't think that's the case. each of my individual strands feel very coarse and strangely bumpy. the roots of my hair that have grown out since the damage are black but the rest of my damaged hair is quite brown. the only thing i'm not facing is hair loss, although i have so much hair that i would almost appreciate losing some of this mess.

what should i do? has anyone faced a similar problem before? i want to grow my regular hair back. please help me.