Thanks once again for all your suggestions. I'm tyring to implement them wherever possible.
1. Though I've informed the school about his dairy free diet, I cant be 100% sure about what he eats there. That might be a cause. (they celebrate the children's B'day parties and serve cake to them)
2.I noticed that he craves sugar (he grabs it whenever possible). Is there any substitute for sugar which I can safely use as a sweetener?
3.He was given antibiotics recently (a month back) for flu.

But anyway, I've stopped Nuxvomica for the past 4 days and the good thing is that he has been sleeping through the night(I hope this trend continues, and I can get my sleep back)!