Hi A.,
You have received lots of advice, some I agree with and some I don't. My son had acid reflux but the silent kind (little spit up but lots of pain which equaled a very unhappy baby who slept very little). Here are some non-medical things you can try now:
1. Breast feed using the football hold where the baby is upright
2. Keep baby vertical for at least 30 minutes after feedings
3. Baby should sleep elevated. If the carseat is working for you, keep using it. A glider could work as well. My son wouldn't sleep in either of these so we ordered a "Tucker Sling" online. It's a wedge that elevates the mattress and a sling that wraps around the mattress and baby (like a burrito) to keep baby from sliding to the bottom of the crib and keep him upright. My son slept in this until he was 12 months old with no problems. Google Tucker Sling and it will come up.
4. I also exclusively breast fed and there's no reason why you should stop. Just be careful of your diet-eliminate all dairy products because they irritate acid reflux babies.
If the Zantac is not working then go back to your doc and ask that your son be given an upper GI (this must be done at a hospital and you may have to see a specialist, such as a pediatric gastroinologist, to have it prescribed like we did). This will determine whether or not he actually has acid reflux. It's not too bad, my son wasn't bothered by it at all.
If he is officially diagnosed with acid reflux then you can get him on some more effective meds. My son was on Prevacid and that worked for him (he was 5 months old before we found the right meds!). Besides Zantac and Prevacid, Axid is also widely prescribed.
I, too, slept many nights upright with my son on my chest or in my lap surrounded with pillows because that was the only way he could sleep. Hopefully you can get the appropriate help for you son before he has to suffer much more.
Best of luck!
S.