Different people have different comfort zones for number of revs per minute when pedalling. IE the number of times you do a complete circle of the pedal every minute.
The range is generally from 60rpm (slow pedalling, hard pushing) up to about 120rpm (easy to push but legs turn real quick – people who ride like this used to be called twiddlers).
Aim for something in the middle rhythm wise. When you say legs are pounding to the dozen do you mean your feet are going round really quickly or really slowly?
If it’s really quickly (not much shoving needed) then try a smaller cog at the back or bigger one at the front, until your feet are going round between 60 and 90 times a minute. Obviously the opposite for if your legs are going too slow.
If you’re strong but bulky (like I am) you’re probably going to be nearer the 60, if you’re lightly built and supple then closer to 90.
Also make sure your saddles at the right height. Roughly speaking with your HEEL on the pedal your leg should be almost completely straight when the pedal’s at the bottom.