Can you use tampons while treating thrush with cream?

No, tampons should not be used during vaginal infection.

Your vagina has a very delicate balance of bacteria naturally occuring that keep the vagina healthy, the acidic pH of the vagina kills 'bad' bacteria while allowing the 'good' bacteria that help keep yeast under control to thrive. Tampons can effect vaginal pH so in turn effect normal bacterial balance, they also allow massive bacterial overgrowth and prevent vaginal cleaning - tampons are a major cause of vaginal infections, using tampons when you already have an infection can make it worse, also if flora is off-balance it is more likely that the bacterium responsible for TSS is also present.

You can use pads (although it's best to avoid commercial pads such as Always or Kotex as they prevent air-flow and contain chemicals which can allow increase in bacteria and yeast - best to use cloth pads like Lunapads or Gladrags), softcups, or menstrual cups. Tampons are best avoided.