Our kitten has eaten chrysanthemums!

Our kitten has is 5 months old and we believe he has eaten chrysanthemum flowers (he was playing/eating a few around 2/3 weeks ago). He also began being let out on 24th July. He began to have diarrhea last saturday (30th July) and has not been let out since. He has been having diarrhea since saturday which means this has been continuing for 5 days. He went to to the vet on monday, and mentioned the plants, but she wasn't to concerned and placed him on Hills I/D but he doesn't appear to like it. Can any advice be given on what we should do next, or how long we should expect him to remain ill for?