Zoe, just found this thread, but really hoping your bubba is improving. I agree with all the positional stuff, but if he's on Zantac, get your doctor to write you a sliding scale of the doses for when your bub puts on weight.
Darcy was diagnosed at birth. I just learnt to smile and go hmmm to all the 'well meaning suggestions' fairly quickly.
We found the zantac great, and finally stopped at 12 months but like the others said, it's variable. I was lucky i didn't have to cut stuff out of my dietand now even Darcy will get a tomato out of the fridge and eat it like an apple.
Do what works for you.