ds had problems with milk - first with formula...was on soya for a while then gradually, very gradualy, got him onto sma..then tried organic cows milk at 12 motnhs - he too had been having it on ceral and in food for ages.
he had the horrible HORRIBLE nappies so put him back on sma til it settled
What i then did was started giving him half of one feed per day with cows milk - eg breakfast milk, half formula half cows and then the rest formula....stayed with this until he got used to it.....4 days...
then added more cows milk than formula in that feed.....left it a bit......then all cows milk...left it a bit again
when that feed was sorted, i did then same with his small afternoon milk and night time bottle. Night time bottle was the last to go
This took about 2 months in total - but was well worth it
now 16 months and totally on organic (or sometimes normal if we cant get to tesco and have to go to local shop )cows milk and is fine. I thik some babies are just a little more sensitive
hope this helps!