Experience points gained when defeating an opponent are proportional to the difference between their character level and yours. If you used the trainer to jump to level 122, you are not going to get any experience points at all from defeating opponents. You can still get experience for completing quests, but not enough to gain another level. The number of points needed to reach a certain level is proportional to the cube of that level (as much experience as it took to get where you are now, it will require 5 times that amount to reach the next level). There are a couple bonuses in the game that will bring you up to the next level, which is the only way you will be able to level (within the game) at this point.
If you do not want to start a new game, you can use
iZakaroN's SaveEditor (or from
Kiya's site, with description) to give yourself some stat and skill points. This program can also edit experience points, but I'm not sure if the game will drop your level if it loads an edited save with lower experience. When raising experience points the change is not registered until the next time you get experience points, so had you boosted your level that way, you would have gotten all the stat and skill points for each level gained.
Now there is just the crash problem with the mage character...
