Red and swollen eyes

My baby is 5 months old and she has been using Enfamil from when she was born until now. Today I fed her normally and after feeding her eyes started to get swollen and red and itchy. I called her Pedi to ask and they said she may have an allergy and to use Zyrtec ( has anyone used this already?) and drink Pedialyte ( has anyone used this already?). I searched these products and Zyrtec is used for 2 years or older and Pedialyte is used for 1 year or older. So I’m confused should I use that or continue to feed her with formula? Because her eyes got back to normal after 1 hour of feeding.