WIC Help!

Hi. We switched our 7w old daughter to Gerber GoodStart Soothe formula from Enfamil Premium Infant due to joining WIC. She’s straining to poop and screaming bloody murder, almost like pterodactyl screeching she’s in so much pain from constipation. I’ve tried doing all I can to help her and I feel horrible like this is all my fault. Her poop is so thick. She’s never had a problem with her other formula, honestly I loved it. If we get a doctors note can we give it to WIC and have them switch it for us? I’ve never heard her scream like this before and it’s breaking my heart. I’ve cried to my husband because I don’t want her in pain like this.