Hair loss help?

Please help me!!! My hair has gotten a lot thinner recently and it s really worrying. I am a 20 year old female but I have a few theories as to why this happened. Firstly I have lost a lot of weight some of it was lost through quite severe calorie restriction. Second reason I haven t cut my hair in about a year and a half. My question is is this thinning reversible? I also dry my hair with a hairdryer and straighten it weekly. I also exercise frequently. My question is is this damage reversible? I m not going to hairdryer or straighten my hair anymore and I m going to start eating more iron and vitamins and zinc and a hair strengthening shampoo. Should I take a supplement too?