My son was the same age when he was first diagnosed with OCD & ADHD. He had thoughts of the family being sucked through a fan and everyone being "chopped up" He was ditraught that he couldn't stop them. I brought him to a psychiatrist. His psychiatrist explained that these were horrific thoughts-- they were unwelcome and that he didn't have the ability to stop them. He did not want them to be true-- he didn't hate us. He was put on medication ( Luvox) which helped to make this managible for him. His psych. also worked with him to teach him about OCD.
He's now 20 years old and doing wonderfully. The other day he jokingly told me that he's learned a way to make his OCD work for him to compensate for his ADHD. It must be working as he made the Dean's list this semester.
I was terrified in the beginning -- but there is help-- it can get better