Ponymum apologies I didn't see your comment earlier about cows milk intolerance but I should be able to give you an idea.
Effy is intolerant to the protein in cows milk, which is slightly different to a lactose intolerance but I believe they can manifest themselves similarly.
There are a range of symtoms from rashes, to vomiting etc. Effy's intolerance is fairly mild, in that she can have up to 2oz of milk before it appears 2 hours later, but her reaction is quite extreme - she projectile vomits every 20 mins until every bit of bile has come from her stomach. Some babies can't even tolerate a drop of milk on their lips before having a reaction, others more like Effy.
If you are concerned you may have problems getting anyone to take you seriously. I spoke to the dr and Health Visitor four times, and this is after Effy had been hospitalised after the first reaction, before I insisted that they arrange for her to be tested. They had just kept asking me to try different types of milk until this point.
When the GP did agree to have her tested, he rang a paediatrician at the local hospital and she said immediately it sounds like she has it and recommended she be given Nutramigen to try. This is a formula milk where the protein has already been broken down somewhat so she has to work less hard to digest it. There are more extreme versions of this, for example Neocate, where the protein has been broken down to one molecule. Luckily Effy was fine with Nutramigen and has thrived ever since.
We have since been referred to the hospital, but in the meantime we are not allowed to give Effy any dairy, eggs or seafood apart from white fish, which has limited her diet somewhat. Cow & Gate do a brilliant egg and milk free pasta which has been my life saver.
On a positive note, 80% of children have grown out of this intolerance by the time they're 4.
Apologies for the length of this. Hope it helps.