Hello,
Contact your hosting provider and ask them about reports of the queries that use a lot of CPU on your site. Provide us with these reports to find out what exactly is the reason for the issue.
Check all the enabled plugins and disable all the plugins that you don’t really use. Don’t keep them enabled just in case.
If you don’t need a portfolio disable it in Theme Options > Portfolio. If you don’t need testimonials disable them in Theme Options > Global.
Regards