Apache 2 consumes >=100% CPU and Memory

My server, on which I have the wordpress installation uses two much CPU. It isn't a constant phenomena, but it keeps happening about each 1/2 hour. I embedded here some graphs of CPU and Memory consumption on my server. Could you please help me fix this?
<iframe src="https://rpm.newrelic.com/public/charts/5WwRAmxFNUg" width="500" height="300" scrolling="no" frameborder="no"></iframe>
<iframe src="https://rpm.newrelic.com/public/charts/6pZF2ps94BW" width="500" height="300" scrolling="no" frameborder="no"></iframe>
<iframe src="https://rpm.newrelic.com/public/charts/lxcwYF0MObB" width="500" height="300" scrolling="no" frameborder="no"></iframe>