The best thing is to figure out what the propblem is and fix it. Do you have access to an LC who can check it out for you?
If you keep feedign without fixing it, it'll just get to the point where you can't feed any more. even pumping can still hurt too..
Does the nipple come out the same shape? Have you tried different holds on that side? Is this the same side you had issues with before? does it hurt all through the feed or just at the start?