how do i get my level over 17.

Use your major skills, I.E. the ones you picked at the starting of the game. When you go into the menus, go into the section for your health bars, I think it's the third tab that shows you your skill levels. The first seven are the ones you want to train in order to level up. Basically for every 10 times you level one of those skills up, you level up. So, for example, if you chose Blade as you major weapon skill, and you're using Blunt weapons all the time, you're going to level up really slowly because levelling up Blunt isn't going into raising up your level.

Correct MM, I always make the skills I use most as my major skills. But I make a custom class everytime.