Auto post creation

I have 3 solution for you,

1. post by emails is enabled:
   go to setting > writing and delete the email which you let it to put posts.
2. some body or some plugin is accessing your username and password:
   change theme all include your main email.
3. use a plugin to confirm post publication:
   if you want to publish a post it gets your confirmation
   if it didn’t get fixed please disable plugins like plugins that feed your website by instagram.

be careful about plugins.

Good luck.