Well, I'm feeling very down with the pain now.
Had an x ray and they cant see anything wrong with it. It has a very big, extremely old metal filling in it. At first it felt 'odd' when I bit down on it and over the months its gradually got worse to the stage it is aching all day, sensitive to hot/cold and even inhaling sharply! It hurts to brush it too.
With my fingernail I can feel a vertical line in the enamel but its round the back of it where I cant see. Would that be the cause? It all looks ok - no swelling or filling breaking off. All observations and suggestions for treatment will be well received.