You do need to see the doctor as this could be thrush or it could be mouth sores (as Nelie noted) from rubbng your irritated toungue against rough spots on your teeth or from another cause (like biting the sides of your tongue as it -- the tongue-- could still be inflamed and a bit larger than normal).

If the former, the best treatment is an oral med, Diflucan, sometimes a Nystatin rinse is also needed. If the sores are caused by trauma, various preparations such as Ulcer-ease, GelClair (or the OTC form, Rincinol) or simple salt/soda rinses will help.

Sometimes ulcers resulting from radiation can be slow to heal due to tissue damage, and they may well need more proactive treatment -- your oncologist should be concerned about this as well.

Gail