What should i do to make my hair grow?

I damaged my hair 4 years ago by bleaching it and getting it permantly straightened. It stopped growing for a while. It still grows, but very very slowly. It has always grown slowly. I havn't cut the length at all for over a year, and it grew 2 inches at most. I wear clip in extentions, and use a ceramic chi straightener daily. I blow dry my bangs, which grow fast, but let my hair air dry. I'm willing to do anything to make my hair grow long. It is about 4 inches past my shoulders. I condition it a lot, use hair masks at least once a week, and use leave in conditioners. Is there a hair doctor or anything like that I can talk to? I'm willing to buy expensive products and try anything to make my hair grow long.