site speed goes up and down a LOT

Hi all,

I want to speed up my site. I'm running on 1.3.9h, and the url is
http://bit.ly/q65NUa

The biggest problem for my site is that the site speed goes up and down a LOT. When I measured parse time yesterday, it was really fast, less than 0.5s for all pages. But sometimes it's a LOT slower than that.

I did everything listed in this tutorial:
https://www.zen-cart.com/tutorials/index.php?article=21
that was relevant to me.
(The only thing I didn't do is checking the 'slow query log' because hostgator does not keep 'slow query logs' so I couldn't look into that.)

And even if I didn't optimize everything, the sometimes-fast-sometimes-slow thing is kinda weird.

Does anyone know what the reason might be?
And in general, for those kind people who took the time to visit my site, do you feel that it is slow?

Thanks!

In a shared hosting environment the most common cause of intermittent slowdowns is a site somewhere on the server that is over-using resources.

PS: I just browsed around your site and the speed seems fine right now.