I've hosted my site on a server provider that I got cheaply. Recently when the traffic to the site increased suddenly I started getting a Database Error and when I try to login to the wordpress dashboard, I'm getting a message that perhaps the username and password in the wp-config.php file might be wrong. So, I logged onto my cpanel and created a new user for the MySQL database and when I replaced those parameters in the wp-congig file, the site started working again but only for a few minutes!! I started getting the error again! And this has become a routine. I'm not able to understand where the problem is! Tried to contact Support but they couldn't do anything either. It worked consistently for a full day when I installed Hyper Cache plugin but then again it was back to normal. Is there anything I can do??
If the password you have configured for the database stops working, and you need to keep creating new users / passwords then I'm afraid someone is changing them.
If you're not - and your hosting provided isn't - then someone else has access to your server ...