There can be several reasons for this. Here are some possibilities to investigate.
- Your ISP is having a period of slowness (check other websites)
- Your web host is having a period of diminished performance
- There is something on your website slowing things down
The first two possibilities usually resolve themselves within a few hours. Some web hosts provide a status page that you can check to see if there are any current issues. If your hosting provider is poor in general then you may notice periods of slowness frequently.
If your website is consistently slow day after day and you don’t think it has to do with your web host, try these things.
- Run the Regenerate Thumbnails plugin to make sure proper image sizes are generated for use by the theme. It’s possible that full size images are being used (possible after a theme switch). The JPEG & PNG Optimization plugin is also worth running.
- Make sure your background image is not more than 500 KB. Smaller is faster. Things can get slow if it’s several megabytes.
- If a caching plugin is used, clear its cache then deactivate it. Improperly configured caching plugins can actually slow down a site.
- Deactivate all plugins to see if the site is running quickly again. If so, the issue is likely a plugin. Re-activate them one by one, testing as you go to determine which it is.
- You can also run the P3 (Plugin Performance Profiler) plugin for clues.
- Check Pingdom Website Speed Test for major performance issues
Here are resources for help:
- WordPress Support Forum – There are many threads matching “slow site” or make a new post).
- Caching Plugins – Keep in mind that most need to be configured properly to account for your specific theme, plugins and server environment. Don’t feel like you must use all options. Test performance after each configuration change you make. WP Rocket is a paid caching plugin that is generally easier to configure than others.
- WordPress Optimization in the WordPress Codex