When hair is subject to lot of chemicals and treatments like straightening,  smoothening,  etc,  it ends up damaging the hair as it loses its protective cover.  It's important to use gentle shampoos and protective serums to prevent further damage.  All these can be had from a dermatologist who is experienced in cosmetic care. U need to visit in person to get a detailed evaluation of the current state of your problem before being prescribed the needed care therapy.