I had to fight through the pharmacy at a Kaiser hospital to get them to recognize the difference between VSL 3 and VSL 3 DS. Like others said, VSL 3 is OTC and DS is Rx only. Very, very, very few pharmacies have any clue that there's a difference. You will have to work with them until they figure it out.
That probably means talking to the manager. The half-educated pharmacy tech won't get you far enough