I need help!

So, my baby girl was born on August 23rd at almost 3 weeks early! She is completely healthy. She started on similac Pro-sensitive at the hospital. Ohio wic will not pay for similac so we decided to switch to Gerber soothe. It was NOTHING but terrible. She began projectile vomiting EVERYWHERE! Then her bowl was extremely loose and she got a terrible diaper rash. We ended up at the ER due to her ped thinking she was dehydrated. Thank goodness she wasn’t but now she’s on similac alimentum. Shes been on it since Friday, Saturday she was up all night scream crying like something was hurting then would vomit everywhere. Then again last night was the same. 😖 someone help!