I think it was something to do with the new shower gel and I had recently exfoliated under there.
It went down after a few day but I should have really gone to doctors as the underam is a gland.
Try using natural deodrant too lush.com do some good ones.
Haven't changed the type of deodorant I use in a long time and always use Sanex or Carex shower gel and the same sensitive shaving gel i've used for years and never had a problem beforehand.
I'll see if changing them helps :) Was wondering if it was a bit of an infection or something as been feeling very run down the last few days and in recent blood tests my white blood cell count has been misbehaving so may be something to do with that.