It may be positional or milk may not be expressing properly First sit in a comfortable position Express a little milk and try again. Even if she doesn't take milk from that breast you can express it and feed her with a sterile katori and spoon. You can get yourself examined by your doctor to see if there is any problem with the breast

Try to find the proper latching technique. Never avoid one side breast feeding.... Atleast try to express out and feed the baby. Needed physical examination to find the reason