how do i stop my hair from falling out (female)?

i've got very thin hair as it is, but recently more and more has been coming out, especially when washing (i wash every 3rd day). huge clumps of hair come out during and after the wash (ie when i comb it). i use organic shampoo and conditioner (so it doesn't have lots of chemicals in), and rarely blow dry. i never brush my hair when it's wet, i always comb, and i don't ever straighten/curl my hair. what might i be doing wrong? might it be dietry? also what can i do to promote hair growth to make my hair thicker? thanks