1. Is this something that is present right away, or can it develop? (would I have seen signs of this in my 1 month old by now, or can it start developing?)
M's was probably present from 4 weeks on but not dx'd until 7 weeks. Look for swallowing a lot while lying on the back, spit up often and (for M) inability to lie flat on his back. He slept in his bouncy chair until about 10 weeks. He still has issues with it, but the pedi put him on Prevacid and Zantac and he's doing much better.
We noticed it around 6 weeks. Got him on Zantac and it is much better. He still spits up but isn't in pain when he does so. Another big sign is arching his back when you try to burp him.
Re: A few Qs about reflux
https://www.pollywogbaby.com/refluxandcolic/refluxsymptoms.html
I found this site helpful. We noticed symptoms around 4 weeks and DD was diagnosed at 6 weeks. She has been on Zantac and has helped a lot!
DS~4 years old~born November 6, 2010 (1st year of preschool)
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1.) I started noticing it in my son around 3-4 weeks.
2.) Excessive spit up.
Spitting up as soon as you lay them down.
Arching back, crying during feedings, but still wanting to eat.
The above are what symptoms my son had.