I really need some answers! why am i constantly having delusions of thinking i killed people as i walk past them and have to always check?

Obsessive compulsive: Disorder. This is likely a form of obsessive can disorder. These are unlikely to be true delusions. Rather, they are what are referred to as over valued thoughts that occur in ocd. I would recommend that you see a psychologist and a psychiatrist for medicinal and psychotherapy treatment of your condition as soon as possible. This sounds like a horrifying condition for you with unwanted thoughts that create a severe sense of dread. Do not fear that you will act on these thoughts.That is not a characteristic of obsessive-compulsive disorder when the thoughts are obsessional.Please get help as soon as possible see you can feel better as quickly as possible. Best wishes.