Why is my hair falling out?

Im 14 and for at least the past month ive noticed my hair falling out in large clumps. I rarley use heat products on my hair and the last time i bleached my hair was 3 years ago(highlights). Today i started taking vitamins just in case i have some vitamin deficientcy. Im not going to go to the dr just to have them draw my blood for my hair. Any sugestions that help keep my hair from falling out untill the vitamin starts working, besides weired things such as rubbing mayo or toothpaste into my hair/scslp. Thanks alot!!