Cows Milk Allergy

Does anyone have a bub with a cows milk protein allergy? If so, at what age did the symptoms start to appear? Our 10 week old has just started having tummy aches, green poo and a bit of eczema on her face. Her sister has an allergy but I can't for the life of me remember when her symptoms started to appear as it took 11 doctor visits until someone took me seriously so she wasn't officially diagnosed until 7mths. At her six week check up, the pediatrician said she would have started showing symptoms so I was really hoping she could tolerate it.