If nursing one side per feeding is not working after a week or so, try keeping baby to one side for a certain period of time before switching sides. This is called block nursing.
Start with 2-3 hours and increase in half-hour increments if needed.
Do not restrict nursing at all, but any time that baby needs to nurse simply keep putting baby back to the same side during that time period.
If the second side becomes uncomfortable, express a little milk until you're more comfortable and then use cool compresses - aim for expressing less milk each time until you are comfortable without expressing milk.
In more extreme cases, mom may need to experiment a bit with time periods over 4 hours to find the amount of time per breast that works best.