So I have fix now.. There's a little cheat to make Derek go down 20 skill levels in all skills. You can do that until you hit somewhere around where you were before, or just go all the way back to skill levels 1. It's up to you..
To perform the cheat, go to the classroom. First open the Bull Fart skill 3 times. Then Door of Regret, Thirsty, Bull Fart, and lastly open Door of Regret again.
Hope this works for you :)