The gum tissue directly above both of my eye teeth has itched relentlessly for my entire life...49 years!!! As a child my mother simply told me to rinse with salt water. This provided no relief of course. My childhood dentist told me that what I had was herpetic lesions on the gums and that was what I was feeling. In point of fact, I had canker sores NOT herpetic lesions. However, the itching has never stopped, not for one minute, for my entire life...even when there were no canker sores present.
As several other people have mentioned here, I've tried everything from salt water to scratching them with sharp fingernails and even straight, 100% undiluted, hydrogen peroxide. At 49 years old I now have huge notches in my gums exactly where the itching has always been due to all of the scratching, poking and injury I have caused over the years, in search of some kind of relief. Any relief I've ever had has been fleeting and has lasted for up to an hour at most.
There are times, like right now, that it's absolutely unbearable. It's times like this that I resort to scratching until they bleed and follow up with crushed aspirin and/or hydrogen peroxide. Both of these help for a short time...but then I'm back to square one again.
As twisted as it sounds, it's been a relief to read that others have experienced this. I've felt like a freak my whole life and have long given up mentioning it to doctors/dentists. Any insight and/or suggestions are more than welcome!
What you describe to me sounds like a bad case of chronic periodontal disease - this is the condition where your teeth become detached from the gyms allowing the bacteria and plaque to pile up in this space which than leads to chronic, but small scale infection (which can lead to sores forming, as you have experienced already). What you need to do is to have a dentist examine the state your gyms are now and to clean all build up that has accumulated in the loosened space. I know that even this might not be definite solution, but at least it's far more better than having only temporary relief.