Exactly!
I am sorry but I just realized I missed something earlier, and it could be important. I went back and re-read your first post from 2 days ago and saw the one vet prescribed carprofen and the other vet prescribed prednisone. Carprofen (aka Rimadyl) and prednisone cannot be used together because it increases the risk of GI problems. They recommend a one-week washout period between ending one and beginning the other, to be sure it is all out of the system. I don't know if the vet didn't read his record to see he had just been prescribed carprofen by the other vet, or if he told you to discontinue the carprofen and wasn't worried because it was only one day of using it (if so I wouldn't be worried). But in case your dog is still on both meds, that is not recommended.
https://www.zoetisus.com/contact/pages/product_information/rimadyl.aspx wrote: CAN RIMADYL BE GIVEN WITH OTHER MEDICINES?
RIMADYL should not be given with other NSAIDs (for example, aspirin, etodolac) or steroids (for example, cortisone, prednisone, dexamethasone, triamcinolone). Tell your veterinarian about all medicines you have given your dog in the past, and any medicines that you are planning to give with RIMADYL. This should include other medicines that you can get without a prescription. Your veterinarian may want to check that all of your dog’s medicines can be given together.
https://www.marvistavet.com/carprofen.pml wrote: Carprofen
INTERACTIONS WITH OTHER DRUGS
Multiple drugs of the NSAID class should not be used concurrently as the potential for the aforementioned side effects increases. For similar reasons, NSAIDS should not be used in conjunction with corticosteroid hormones such as prednisone, dexamethasone etc. Pfizer recommends a 5-7 day rest period when changing over to carprofen or to another NSAID from carprofen.
https://www.marvistavet.com/prednisone.pml wrote: Prednisone
INTERACTIONS WITH OTHER DRUGS
Glucocorticoid hormones should not be used in combination with medications of the NSAID class (ie aspirin, carprofen, deracoxib etc.) as the combination of these medications could lead to bleeding in the stomach or intestine. Ulceration could occur.
http://www.dodgerslist.com/literature/IVDDcourse/conservative_treatment.html wrote: Caution: Steroids and NSAIDs must not be given together or one after the other without a safe washout period of 4-7 days.
If your dog is on both carprofen and prednisone right now, I would not give him any more carprofen until you ask the vet, preferably not the vet that prescribed the prednisone because it looks like he's the one that missed it or wasn't practicing safe use of the meds. I wonder if that is part of the problem with his soft stools.