Why does my hamster keep getting wet tail?

i got a female syrian who 2 days after purchase had to go back to the store for treatment for wet tail. They kept her in and i got her back just over a week later. Then 6 days after bringing her home, she had it again and so this time the vet gave me the treatment to give her at home. I did this for at least two weeks and she looked like she had cleared up. However, after being clear for maybe 5 days or so, i noticed this morning she has started to get it again. Im worried she will just keep getting this and that it is not a nice way to live for her. i have tried changing her diet and cleaning the cage but she just keeps getting it. What do you suggest i should do?