It can be an intolerance, which can often have no rashes.
Many doctors only think of allergies and then only if they show up on tests.
Your child have have huge issues with milk protein and have it never how up on an allergy test.
I will try and find you a really good link on allergy/intolerance. I can't remember where it was so it may take a while.
You could also go to
http://www.allergy.org.nz and have a look, it may tell you something there.
I think the big thing with Emily was the milk hitting her tummy - I have never heard another baby do this.
As for a manuel - my Emily defies all logic and explanation! DD1 was textbook and so I thought Emily would be to - boy was I wrong. She has tuned all my parenting ideas and expectations upside down. It has probably been quite good for the anal control freak in me to have to loosen up and let go.