There is a problem I am having with believing in god can you help?

Do you think god is willing to prevent evil but he can't but wouldn't that prove god is not omnipotent? But if he is but he doesn't want to then wouldn't that make him a @$$hole? If you say he wants to and he is stopping evil then why is there evil in the world? But can he not stop evil or he doesn't want to? Then why should we call him god?