I had this exact same thing (the blisters not the mastitis) about 2 years ago. It turned out to be hand, foot and mouth which I caught of my best friends little boy.

I was in absolute agony!!! The only thing I felt helped was sucking on ice cubes and gurgling them to the back of my throat, I did it constantly and then it numbed it.

Get yourself to a doc asap and stay away from anything acidic - I learnt that the hard way!!!