Hi G.E.H93. Welcome to the forum, although I'm sorry that you join when you're obviously scared something is wrong.

I am not a doctor and I have no medical qualifications. 

My dentist once advised me that anything strange in the mouth that lasts for more than 4 weeks should be checked out. Also, mouth cancers in the early stages are often painless, so the fact that your spot is new and painful could actually be good signs. Also, you're a non-smoker and under 50, which also reduces the risk of mouth cancer. 

This might be something called an "aphthous" ulcer. The Americans call them canker sores. They are white spots which can appear anywhere in the mouth, and they're incredibly painful. No one knows what causes them - they just pop up, hang around causing misery, then start to heal and go away leaving no scars. Most heal up after two weeks, but some can hang around longer. 

You could try treating the spot as if it's an aphthous ulcer and see if it goes away (if it's cancer, it won't go away).  There are several treatments you can try. Personally, I use Oraldene mouthwash several times a day, together with direct topical application of Boots own brand mouth ulcer gel to kill the pain.  Put the gel directly on the spot and it should kill the pain immediately. 

If you try this and you still have it in another two weeks then see your doctor or dentist without further delay. But if you can't stand worrying any longer, or want a definite diagnosis then see your doctor or dentist now - whichever one can see you earliest.

Please let us know how you get on.