I get mouth ulcers all the time, so I know that they can be a b*tch.
I don't really find that any medicines help me - I pile on Bonjela till my mouth is numb but it seems to do nothing, and as for those things that are like sand, its unrealistic to be able to have that stay on that spot in your mouth for a long period of time.
Personally if I have a mouth ulcer, or feel one coming on (I can feeling one coming on now actually!) I pile myself up with vitamins, and fruit and veg. Mouth ulcers are caused by poor diet, and especially lack of vitamins (although in your case it does sound like its something to do with you're wisdom tooth).
But if I have a mouth ulcer I buy some multi-vitamins and take one a day (or even two) and then I eat as much fruit as I can. It actually hurts to eat fruit because it is so sweet and acidy on the ulcer, but it's that type of pain where you feel like it's doing good (if that makes sense)
I find that this works a treat and the ulcer is gone in a few days.
The Watermelon Frost is a new one to me - is it good? Must try that in future!
EDIT: Also worth mentioning that you need to have a clean mouth as much as possible to stop bacteria getting into it, so brush you're teeth and rinse as often as you can throughout the day