A canker sore on the tongue can be really painful.
It's one of those situations where even the smallest little tiny sore can seem like a huge great crater. There's something about the way the tongue receives it's nerve supply that makes a small problem area seem huge to the brain. The tongue moves all the time too - causing the ulcer area to rub against the teeth or against food you've just eaten .... youch.
Try this remedy for a sore on the tongue - it's very effective and once you've tried it you will use it all the time: Buy some hydrogen peroxide for mouth use from your local pharmacy. At bed time you need to brush your teeth and gently over the area of your tongue where the sore part is - take care to rinse all the toothpaste residue away when you are done.
Keep your tongue lifted up for a second or two until it gets dry and then take a Q tip with a drop of the peroxide liquid on it and dab it straight onto the sore. Hold it there for sixty seconds and then remove it.
When you wake in the morning the mouth sore will have shrunk and should heal up within a day.