Treat potential reflux and allergy before Dr. apt

Our son (our first child) just hit 4 weeks and has gone from being a generally “normal” to generally “colicy.” He cries constantly, arches his back, wake himself up to cry, is inconsolable, etc. Earlier this week we took him to the ER after he couldn’t sleep for 14 hours straight due to discomfort. After some blood work, a urine test, and a stomach x-ray, the only thing that showed up was a distended stomach full of gas (no bacteria or viruses or sign of UTI). The next day, we took him to our pediatrician who suggested we switch to Enfamil Gentlease from Similac Sensitive. After a couple of days and no change, we again spoke with our pediatrician who suggested we schedule an appointment with a gastroenterologist. With the gastroenterologist appoint 1 week out, and continued discomfort for our son, our pediatrician wrote us a prescription for Zantac to get us through to the gastroenterologist appointment.

Questions:

1. How “safe” is Zantac for infants? I did some research on the web and it seems to me that Zantac has limited risks if used properly (i.e. the pros outweigh the cons it seems).

2. Should we also switch to hypoallergenic formula like Enfamil Nutramigen or Similac Alimentum before the appointment with our gastroenterologist 1 week from now? I’ve been flipping through a book called “Colic Solved” and it suggested infants with “colic” often have either reflux or an allergy to milk protein. Since we are already going to start treating for reflux with the Zantac prescription, should we also switch to a hypoallergenic formula too? Hopefully in 1 week, after the gastroenterologist appoint, we will have more concrete data/tests to guide our treatment plan. I just wonder if I should start treating both reflux and the allergy in advance of the appointment.

3. Do you have any preferences between Enfamil Nutramigen or Similac Alimentum? Is there another formula that is preferred by you?

4. Is there anything else we should do for our son during the 1 week before our gastroenterologist appointment?

Any/all advice appreciated. Thanks in advance for your feedback.