maybe its just your body adjusting?
did you used to go to bed on a really full stomach?? (i did! it was always full!!)
if so, that makes you fell sleepy, and would of helped you fall straight to sleep,
now however your not so full, your body has got to adjust to getting to sleep n its own, rarther than from all prots and carbs in you making you sleepy.
just an idea?? x