It could be wind or your milk supply could be low at night. Maybe you could try increasing your supply.

There is a good book by Elizabeth Pantley called The No Cry Sleep Solution, it might be worth a look. Her website I think is www.pantley.com/elizabeth. If this is not right try and google her name and see if you find it.

Good luck and I hope you both get some good rest soon.

I too went through this at nights.I found out when y baby was eight weeks old that his tongue was tied. He wasn't getting enough milk. I switched him to a bottle and he became a happy and sleeping baby.