WordPress very slow

Slowness/high CPU usage could be due to (but not limited to):
– A poor or memory intensive theme. Switch to the WordPress default theme and test loading time and see if you see a difference. If you do, may be your theme can be re-written to be more efficient.
– Poor or memory intensive plugins. One by one disable plugins and test loading time and see if you see a difference. If you do, may be that plugin can be re-written to be more efficient.
– your server is slow (e.g., “process hang”, overload, you get a lot of visitors, other problems, etc.); generally, every inexpensive host out there is slow.
– I don’t know if you use CloudFlare or not but if you do I would suggest deactivating it and seeing if it helps. Also sometimes a good purge of the cache on CloudFlare can help.
– Lots of images can cause slowness. Also images loaded without compression.

Test your site at (free online testing):
http://gtmetrix.com/leverage-browser-caching.html OR http://www.webpagetest.org/
http://tools.pingdom.com
https://developers.google.com/speed/pagespeed/insights/

Also, review these resources:
– http://www.wptavern.com/determining-which-plugins-are-slowing-your-site-down
– http://wordpress.stackexchange.com/questions/656/is-there-a-way-to-measure-server-resource-cpu-usage-by-wp-plugins/
– https://wordpress.org/plugins/plugins-speed-test/
– try installing the Query Monitor plugin and seeing how long the queries are taking.
– http://www.wptavern.com/my-performance-woes
– http://codex.wordpress.org/WordPress_Optimization
– http://codex.wordpress.org/High_Traffic_Tips_For_WordPress
– http://codex.wordpress.org/WordPress_Optimization/Caching
– http://codex.wordpress.org/WordPress_Optimization/WordPress_Performance