I've just worked out what the burning sore feeling is under my tongue and along the inside gum. Finally got a good look in a mirror and yes, it's thrush. It's been building over a few weeks, starting with mysteriously losing my taste for sour things and feeling a funny change in skin texture in my mouth. Then starting yesterday it was painful to move my tongue.

Surprisingly, I haven't seen it mentioned here much, but it's not a nice thing to talk about. A weakened immune system from prednisone causes it.

@besmith57 did you have to reduce the prednisone while taking the Nystatin? Prednisone and anti-fungal treatments interact with each other, apparently.