formula switch? allergy

Jessica
Hey ladies, so my LO was diagnosed with a cow milk protein allergy at 2 months and we were told at 6 months we could switch back to a regular formula we've been on similac alimentum so we are like 2 weeks away from her 6 month Appt so we tried a different formula so when we go to the doctor we would know if it would work or not. Well we started it yesterday night and she already started spitting up and the spit up looks undigested and when she pooped it looked the same undigested and her belly has been making some serious noises , is this normal when you transition back to the old formula or is it possible she is still allergic? Thank you in advance!