I had this a few years ago and it was due to having a stupid-low iron count. my nails were also breaking all the time. I had iron tablets but also took Sea Kelp and I think it really made a difference. you can buy sea kelp from health food shops. I recommended it to a woman at work who had very thin hair, and she was really delighted with her hair growth.
my hair has made a full recovery, and is also long and curly, although I had quite a few inches off as the new growth was fuller and healthier.