Hi as121,

First, welcome to Psych Central (PC).

It sounds like you're currently exhibiting obsessive-compulsive disorder (OCD). This usually manifests in a cycling of thoughts and behaviors (like repeatedly checking locks). I strongly believe that you're not paranoid (paranoia is a more general belief of persecution). No one knows the cause of OCD, but you did say that you were suffering from depression before the checking began. Furthermore, you said that your mom has mental health issues, so a predisposition is a possibility. There is empirical data that shows high correlations between certain mental health disorders. That said, even an 80% correlation does not equal causation.

You might want to look into cognitive-behavioral therapy (CBT). This is a type of psychotherapy that focuses on thoughts and behaviors.

Again, welcome.