Kitten has diarrhea and normal poop?

Hey guys, I am new to this sub and Hope someone can help me:)

We recently got a kitten, he is almost 4.5 months old. Some weeks ago he had diarrhea and a dirty butt because of it, we went to the vet and he gave him 3 injections to cure an infection. Turns out he also had stomach so it was likely that he had an infection or something like that. The vet also gave us some wet and dry food, as well as powder for restoring his digestion (ig?). His diarrhea went away.

Some days ago I noticed that his butt was dirty again. I checked his poop and it seemed normal.

His butt was stinky and dirty again today, so I took a look into his litter and I saw that he had diarrhea again;( He had normal poop as well from the same day. It seems like he has both of it. Did anyone else have this problem? Is it normal?

Thank you very much in advance!