Sundae, it happens after pregnancy because of a drop in oestrogen. When oestrogen drops suddenly, it does all sorts of weird things to your body, including stopping your body from producing serotonin - and we all know that's the happy drug we make ourselves - so check your moods and emotions and see if there's any correlation between hair fall and your moods.
Post pregnancy though, it's also associated with hair coming out of a 'resting period', but in a big way.
Hopefully my hair will all grow back nicely after a few months.
I'm sure yours will too Sundae. xx