Webs doesn't show temporarly

[avispa987]

Hi everyone. Im having an issue... for example y type my web url that its on my vps.. and the site doesn't show... Then i put in my browser my vps ip, it takes looong time to load, then when it load all my websites are visible and can run...

My cpu load is at 99% idle. its running with one dedicated core of a quad core server... It has 368MB of ram just for two sites...

Can any1 tellme what's the issue? What logs i should post?
Can be one of my sites being ddosed?
How can i test if my vps has enough bandwith ?

Thanks in advance