Apparently Random Site Outages

Hi all, I’m experiencing problems lately with my site (www.puredoxyk.com) becoming unavailable — the whole thing getting 500 Internal Server Errors, main page and Admin console both — and I can’t figure out why. Now, I used to see those errors occasionally, right after I posted, or I or someone else posted a comment, but they would go away with a refresh or two. What’s happening lately is that the site has been down for hours at a time, and my hosting guys tell me it’s definitely WordPress, since my domain continues to resolve and the content is accessible via php scripts. This has happened twice in the last three days. It’s back up at the moment, but nobody knows what fixed it. I’ve just announced the publication of my book, so I’m a little concerned that it stays up!

The first time it went down, I had just posted a text-only post. The second time, I hadn’t just done anything — it was up, I checked a few hours later, and it was down.

I upgraded about a month, month-and-a-half ago, and there were no glitches at all during or since (until now). The most recent change I made was to update Akismet, but that was also almost 2 weeks ago, and the problems didn’t start until three days ago. I don’t have a ton of spam, either — when I checked there was only 12 in the Akismet box, the rest having smartly auto-deleted. I’m running the following plugins: Akismet, Dean’s FSCKEditor, Democracy, Dunstan’s Time Since, Easy Tube, Flexible Upload, Livejournal Crossposter, Live Preview, Subscribe to Comments, WP Database Backup, WP Captcha Free. All seem to be functioning well. I’m using the ZaZen theme with no widgets.

Also, we checked the server logs, and there are no errors on it other than some mentions of an unexpected end to headers (sorry I can’t remember the exact wording), which my programmer hubby says is just due to the load of a page failing.

If anybody has an idea what might be happening here and how I can fix it, that would be MARVELOUS.

Thanks!