that would be the most likely reason - trigger would cause an egg to be released from the follicle whether it is mature enough or not - and would trigger the hormone cascade that leads to AF (progesterone up, then it drops off for AF to arrive). if you didn't have the trigger, and egg was not mature, or the clomid didn't make your body respond appropriately, the follicle will simply have reduced back to nothing - i guess it would be a failed clomid cycle as the clomid itself didn't make you o (which unfortunately happens with lots of us)

sorry to be the bearer of bad news...

BG