Why is my kittens tummy so big?

I took her to the vet last week thinking she was bloated from worms but they did a fecal test and she did not have any they have her on a diarrhea medicine. for the past few days her tummy has gotten bigger and I can feel sort of a harder ball on her left side of her tummy she was just at the vet and they didn’t say anything should I be worried PS she is six weeks old and was taken from her mother when she was two weeks because her mother got hit.

update:

she passed away this morning as we were getting ready to leave for the vet. thank you guys for your help:)