How have you been wearing your hair since the last time you washed? It might just be that you're noticing an accumulation of normal shedding. Sometimes when I wear a bun for an extended period of time, I don't even bother combing it. I just keep spraying it with leave-in conditioner and smoothing it back. So the hair that I would normally shed daily, doesn't go anywhere. But when I finally wash it or rinse it in the shower, I see it all at once.