Well it sounds like it could be a few things. It could be the product you used in your hair, the repeated dying or the heat damage. Maybe you should lay off all of those things and see if your new growth grows in curlier than the damaged parts. If your new hair does grow in curly at the roots then it probably isn’t hormonal it is probably due to damage. If it doesn’t grow in like it use to then you could see a doctor and make sure everything is okay.
A while back I purchased one of those Babyliss flat irons from a salon and when I got home and tried it out on one small section of hair it burned my hair a bit so I took it back immediately. I don’t flat iron my hair much anymore but that flat iron definitely did not work for me.