CPU Overloading

Hi,
For the past week I have been experiencing serious issues with this website, beginning with complete crashes and 503 errors. I made some changes and stopped these happening but am left with lots of server issues. When I deactivate the Shippet plugin, CPU returns top normal, but when activated it jumps around in the red, even maxing out at 100% CPU at time.

please can I get some advise on this and how can I stop this?

The page I need help with: [log in to see the link]