I have had this happen 3 times, first time was last year I was using Tre-semme shampoo and conditioner to trial and it made my hair fall out! Had to change back to Clairol to make it stay in. It started doing it again last year after I had a m/c and a couple of months ago when I had a chem so that would have been from hormones. When I was trialling the Tre-semme I was also stressed from witnessing my friends pre-term birthed baby

So: Shampoo, stress and hormones - YUP being a women is great.

It should naturally do it's course and be done, if you're overly concerned then visit your GP.