Reflux question

We’ve been on Zantac for almost a month and it’s been really good until yesterday. Last night we projectile vomited and we just did it again, so much so I had to hold him toward the ground so he wouldn’t choke cause he couldn’t breathe. Would it be something I ate or could it be that he’s grown immune to the medication? I’m waiting on a call back from my Dr but was wondering if anyone has been in this situation?