I'd ask about the Diarsanyl as I've used it with success. It's a 3 day thing, a sort of glue paste muck you put in their mouths. Only would be suitable if the vet wants to stop the diarrhoea - if they think he needs to purge himself of something rotten, it may not be.
Has Charlie had probiotic before? I checked my notes and Swampy got tum troubles (soreness, not diarrhoea) from taking it once. May be worth asking if it's at all possible that the probiotic may have loosened him up again.
Here's hoping for no more runs and a settled tum today. Have you maybe tried i/d as well?
xxx