What Causes Allergy Like Hives On Face When Eating Cerelac In An Infant?

My Baby is 6 month+ and we just started giving him Cerelac wheat milk and Nan Pro 2. But after day or 2 he started allergic reaction when having Cerelac wheat and then again Nan? Allergy is occuring in face like a hive. So we consult our doc and he prescribed Cerelac Rice, so we changed and allergy after eating Cerelac is pretty less only one or 2 dots in face near the lips. But again after having Nan allergic reaction happened in the whole face like a hive. We consult our doctor and he suggested to stop Formula milk for 2 days and given anti allergic drops (ATARAX). Now my question is do we need to change it to some other formula milk like Dexolac or Similac, does that solve this allergy issue for my baby?