Axid (and the other H2 blockers) are very weight sensitive drugs so it’s possible she’s outgrown her dose. She may need a higher dose or she might do better on a PPI medication like Prevacid or Zegerid. My daughter was on Zantac (like Axid) and she never had lasting relief even after several dosage increases.
Of course the formula could also be the problem. Many reflux babies are also MSPI (milk / soy protein intolerant) and they require a hypo formula like Alimentum, or even an elemental formula like Neocate.