[Moderator edit:  the original post in the thread was cleverly disguised signature spam and has been removed.  Leaving replies, of which this post is the first one, here.]

B vitamin deficiency is usually the main culprit. I've dealt with mouth ulcers (canker sores) all of my life, and even started getting them in the same spot on my soft palate. Diagnosed as a viral aphthous stomatitis (recurring ulcers), antibiotics have no effect on viral outbreaks. Everyone has the herpes virus to some extent, but healthy immune systems keep them suppressed.

Anything with alcohol such as NyQuil is a really bad idea. Alcohol will only dry them out and make them more painful. In order to heal, the ulcer needs to develop a clear coating of mucus.

* Take a B-Complex vitamin with your meal every day.
* Do not drink coffee, alcohol, or anything sweet. Sugar is another thing which will hinder the healing process of an ulcer. If you drink tea, drink it without honey or sugar!
* When they start to sting, gargle with a magnesium-based liquid antacid (don't bother buying the expensive stuff--you'll be using it as a mouthwash). Magnesium works wonders for relieving the pain of ulcers. Just remember not to swallow any of it, otherwise you'll have the runs later on in the day. Magnesium shits are no fun!
* Stay away from overly spicy, or crunchy foods that may scratch your throat.
* Stress can also induce these things, so make sure you're getting a full night's sleep.
* Lots of leafy green vegetables (vitamin K) are also good for healing ulcers of all kinds.
* Buy a humidifier and run it at night by your bedside. The moisture you breathe in will really help these to heal much quicker because it's letting the tissue form a protective coating over the lesions.
* Keep your mouth clean. Gargle with non-alcoholic mouthwash (Biotene is good). Bacteria contribute to inflaming the tissues around the ulcer, so the fewer cooties you have in your mouth, the better.

Now that I know what causes ulcers, I know how to treat them. Mine heal up in days instead of lingering for weeks, plus I get them much less frequently.

I have the same problem that you have, and my doctor told me that the main cause of canker (sp?) sores in your mouth is stress.

As far as you saying that you had over twenty in your mouth at one time, I also had that exact same problems, accompanied with a fever and just not "feeling well" (I was about 17).  I went to the doctor and they said that they were caused by a virus called foot and mouth disease (like hoof and mouth disease, weird, I know), or the MONO virus..

So, in short, there are multiple reasons they could be happening.  Hope you get to feeling better!  I know they hurt like the dickens!

Any chance you are taking Arginine or L-Arginine rich foods?  This can increase ammonium levels and help these kind of viruses thrive.  There's a lot of info to  Google on this - just look up things like Arginine Diet or Lysine Diet, etc.