steve_b77 - Member
I'm no expert but if your saddle is that far back already your frames too small.
You're right, you're no expert 
You could be right but you may well not be.
As TooTall said though, sore backs can be caused by loads of things - one of which is lack of flexibility/core strenght and/or a front end that's too low. Another is pushing gears that are too high rather than spinning.