Thank you for the reply. My mistake for the post :)
Actually, the vet said that probably he is still having parasites. However, it takes time to get rid of them. The problem is how to control the diarrhea for one more month or more until the cat gets clean.
I will post it in the dog-cat section, hopefully someone could give me some advice.
10x
Your post would do better over in the dog & cat section, but I can make a comment. I had an older dog that tests showed he was clear of worms, but by golly, next time he did number two, I saw a live worm in it. So, back to the vet and better worming meds. This means that a test can say the animal is clear of worms, but maybe your cat is not! I also went about cleaning up his poo for about a month, to prevent reinfection.
Also, obviously you should sterilize his litter pan and feed/water dishes, and if he goes outside a lot, check around the house for any rodent carcasses and bury them. Consider giving your cat a quick bath. If he just recently became an adult cat, could be he's developed an allergy to milk. Also, you could ask the vet to do an X-ray of your cat's abdomen, in case he's stopped up or has a benign growth or something odd going on, just in case.