I noticed that Ranitidine and Cemitidine (Tagamet) simply don't work as well as PPIs. I also don't know how safe any of these are while you're pregnant. I'm certain that PPIs aren't good, because they can cause malabsorption, which might harm the baby.
I don't know the answer to taking antacids after taking Ranitidine (Zantac). I just know Ranitidine does nothing for me.
Check with your doctor before doing this, but many people drink aloe vera juice diluted with water to treat their GERD. Others swear by doing the same thing with apple cider vinegar. I'm pretty sure they're okay to use in small quantities even while pregnant, but just check with your doctor before attempting.