When is it time to move on to PPIs?

Hello,

Our 4 month old son is currently on Zantac 15mg. He's been on it for about a week now and we're not seeing any significant improvement. I know a week may be too early to see any change but we're getting nervous and don't want him to end up with esophagitis or something worse. GERD is very new to us because our baby did not show symptoms or refuse feeds initially, this all started about three weeks ago. So we are trying to educate ourselves and ask questions.

When do we know it's time to move on to proton pump inhibitors? We have  a follow up appointment with our son's pediatric GI specialist on April 22. Should we ask him to do an endoscopy (he didn't do one initially, he just sent us for an upper GI series) so that we can make sure our son doesn't have esophagitis? Should we ask him to try our son on a PPI? I have heard both good and bad things about PPIs so I'm very confused. I know all babies are different and a bad experience for one doesn't necessarily mean a bad experience for another. Is Prilosec suspension a good one to try? When is a baby's GERD considered severe enough to make them a candidate for Nissen Fundoplication? If anyone can answer these questions I would greatly appreciate it.

Sandeepa