YaBB SE / major slowness in last few weeks

I have a php-based YaBB SE forum on one of my Dreamhost-hosted sites, and in the last few weeks it has intermittently ceased to function (the pages just do not load, and eventually time out). Over the last few days, it’s been down more than up. In the year plus prior, I had no such problems. Any idea what could be causing the problem? Today and yesterday in particular have been totally miserable.

I did see the notice from Dreamhost that there was a php upgrade. Could this be at the root if the slowdown? I think the problem started about 3-4 weeks ago, but has gotten progressively worse since.

Here’s the forum: