My oldest son (now 36) used to projectile vomit. It was really scary, especially because the move 'The Exorcist' had just come out.
He didn't have this happen after nearly every bottle, however. I'm so glad you are taking him back to the doctor.
Have you tried just letting him have an ounce or two at a time but very frequent feedings- so there won't be so much to come back up? Remember that this is NOT medical advice, just a grandmother's thoughts. I know that you will get this worked out, and someday you will be writing about this memory on a message board, too.