I've never had a canker sore, but I did a quick Google (Google Geek am I!) and found out this:
1) Toothpastes and mouthwashes that contain the foaming agent sodium lauryl sulphate (SLS) can cause, or have an aggravating effect on canker sores. Check your toothpaste!
2) Over-the-counter numbing products can really help the pain. Look for those that contain benzocain, benzoin tincture, lidocaine, camphor or phenol.
3) Anti-bacterial mouth rinses (such as Listerine) are supposed to help speed up the healing of canker sores.
4) Some people find that swishing a teaspoonful of Milk of Magnesia and Benadryl allergy liquid (diphenhydramine) mixed 50/50 over their canker sores (then spitting it out) four to six times per day helps minimise the pain.
5) Herbal remedies thought to relieve anxiety -- such as chickweed, violet and rockrose -- have also been found to be good treatments for canker sores.
6) Daily consumption of the bacteria lactobacillus acidophilus is believed to help prevent outbreaks of canker sores. A good source is yogurt -- but make sure your yogurt contains an active culture of acidophilus.
Don't know if any of these will do the trick for you, but I hope so! Hope you feel better soon.