I know this might sound crazy...but it could also be....worms.

This was happening my youngest (the wriggling, the crying out etc). i was putting it down to teeth as well but it seemed as though the pain meds werent doing a thing. then about a week in my eldest came in to our room and told me that her bum was itchy. we wormed everyone the next day and voila! it was something that never crossed my mind but might be worth considering especially now that your eldest is at school (our case conincided with school as well).

But, even still, i would be tempted to not move her. although the frustration in not having any down time can be hard to bear I have found. what a pity that there isnt a closer bedroom!