It seems your wordpress site using lots of queries per hour. 000webhost has limits on queries because we just provide a free, testing platform.
Personally, I had this problem few months ago, and the reason was, I had put a query inside a loop. (However I didn’t use wordpress). You can check whether your wordpress code has something like that or contact wordpress support in their site.
However, we have seen that this error occurs depending on how wordpress uses the db. So, If you have a big WP project, the only way is upgrading to hostinger.