Grow thick hair back

I need advice! I used to have such thick hair. Until a few years ago it started to thin out. I fully believe it was the birth control pills I was on. I stopped birth control in September so now I believe my hair is on the rebound. My question is what can I do to help it out? I want my thick hair back!! I also cut it 2 years ago just above my shoulders so I would like it longer again too.