I've been there... Hang on! Assisted livings have such vague regulations (at least in Washington) that coming from any other nursing environment, it appears to be a madhouse. And sometimes, AL is an easy trap for nurses to become lazy since it's a very independent role as a nurse.
One of the first things I would do is hold a meeting for all staff who assist with medications (med aids/techs or nurses, whichever your facility uses) and let them know your expectations for quality of work, missing meds, missing blood sugars, unexplained med exceptions, MAR holes, etc...
When I started this AL position, we were behing on service plans as well, so I'd recommend to start scheduling them and type up a schedule. Our assistant-admin (or business office coordinator) did this scheduling. I did an intensive 3 weeks of catch up where I'd have 4-6 care plan meetings per day, it was exhausting! But, it got the work done quickly and it helped me learn the resident population and their families.
As far as the narcotics, I ran into this as well... But, this can differ between what tiers of controlled substances want to lock-up. My current facility was not locking Ativan, but I changed that. Like the previous poster said, documentation is going to be your best friend! Save the memos you create for all the in-services and have it signed by all employees to show you are working to clean up the facility and it's mistakes... For as unregulated as the AL community is, it's incredible how far administrators and nurses let them fall! Keep up the good work! It just takes time.