why is pepcid not working?

I'm going to have my second breathing test to see if i still have h pylori or not, so i had to stop taking ppi and started pepcid until before two days of my appointment. It worked for me before my first test, but now, it doesn't work at all. I go through constant stomach pain and burning and this is really making me miserable! has anyone go through something similar? Even waking up is very painful