Heather, that sounds like white spot. It is reasonably common - basically like a blocked duct with a bit of skin over it. Some women use a sterilised needle to lift the covering skin back and then pull out a string of dried milk. This usually relieves the pain, but white spot does tend to be recurring. The ABA helpline can give you more info if you are interested. The GP should also be able to lift the skin up and clear it for you anyway tomorrow so it's fine to leave it until then.

GL.