[bashy]

If you are on a shared server, speak with your host...
Tell them what server loads you are getting and they (if good hosts)
will look into this, It might just be something simple such as another
site using too many resources and your host once prompted will pick
up on this and resolve any issues....

So, if you on a shared server (shared hosting) speak to your host asap
State that it is really slowing your site down and something needs to be
done asap as the quality of service you are offering your customers is being
affected by the server performance...

Im sure you get the idea....
Hopefully this will be the case and it will be an easy fix for you...

Good luck!!