Please can someone give me some advise?

i took my daughter to the gp today cus she was chesty she had a cold and she had terrible colic and conjuctivitis and also chickenpox the gp gave me eye drops colic drops and nasal drops he also advised me to change her milk from cow and gate to another one i decided to change to farleys well now shes got a rash just on her belly it looks like an allergy reaction i called the nhs direct they said the colic drops eye drops and nasal drops dont give allergy reactions so its got to be the milk so now ive got to get sma but wont keep changing my babys milk make her worse as anyone been through the same situation as me or got some advise please my baby is 8 weeks old