Have Cat Questions? Ask a Cat Vet Online.
I am sorry to hear you are worried about Jack. I am a veterinarian; my name is ***** ***** I will do my best to help.
Have you had a stool sample checked for microscopic parasites? That is the first thing I would do. If he has a parasite we see in kittens called Coccidia, a course of Albon should take care of his runny stool and gas.
If no parasites are found, a medication called metronidazole may be helpful. Probiotics might help (beneficial bacterial supplements) like Fortiflora and Proviable.
I would also consider a bland diet like Hills I/D or Royal Canin GI for awhile. These are "prescription" diets you can get from a veterinary office or a website like Chewy.com (but they will contact your vet before they ship it to you).
Let me know what other questions you have.
I hope you were able to see my answer; can I help with anything else?
How is Jack today?