502 Proxy error?

I just created a new wordpress blog on http://www.marissainamerika.nl and most of the times it works just fine but like 1 in 20 times I load a new page or something I get this message

Proxy Error
The proxy server received an invalid response from an upstream server.

The proxy server could not handle the request GET /index.php.

Reason: Document contains no data

or this message:

Error establishing a database connection

This either means that the username and password information in your wp-config.php file is incorrect or we can’t contact the database server at localhost. This could mean your host’s database server is down.

* Are you sure you have the correct username and password?
* Are you sure that you have typed the correct hostname?
* Are you sure that the database server is running?

If you’re unsure what these terms mean you should probably contact your host. If you still need help you can always visit the WordPress Support Forums.

And this lasts for a few minutes and than I can use my site again, but it sucks because I never know if my site is going to work or not.

can anyone help me with this??