Well I say lump, but it's more like a little raised patch, about the size of a 20p, and it itches like mad.
It is by the waistband of my jeans so i think that is making it worse, and it doesn't seem to be getting any better.
I googled red itchy rash and it came up with Scabies , pretty sure it isn't that though, the rash looks different and it hasn't spread.