Thats a tough one. You would think the Losec would stop the acid smell. I would be inclined to think he may be a little sick and bringing up abit of bile or something when he chucks.. hence the smell.

Have you eaten anything different that could be adding abit more "acid" so to speak in your milk? I think the cuprits are tomatoes and citrus.. (i think there is more but i cant think of them off the top of my head).

If it doesnt pass soon.. they may need to increase his dose.