My Stone Pizza oven needs help?

I have an outdoor stone pizza oven. it was built last year. From the start it seemed to take too long to cook a single pizza, but after we reused it this year it doesn't seem to be reaching even the same temperature with the same size fire or by any other method we have tried. It is a bit frustrating because it feels as if the stones on the mouth of the oven, which are not firestone, are reaching a higher temperature than the ones that are firestone. So my question is, Are there any solutions out there for this problem that avoids gutting my oven out. Are there any stones that we should buy to line the oven on top of what we were told were "firestone"? Is there any fire-building method that makes a hotter fire? Do particular wood types produce more heat than others? Does placement of the fire before and during cooking affect the internal temperature and if so what is the best method?