Need help with an error on a multi-site

We are getting the following when trying to edit a any page through the dashboard:

Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 25428327 bytes) in /home/admin1/public_html/wp-includes/wp-db.php on line 885

It is multi-site, membership and commerce site using Marketpress.

the membership sites are not experiencing the error just the main site. The site worked for the last 8 months but now this problem.

The membership had not grown and no new plug-ins were introduced.

Host Gator tells me they can not increase the php memory on a resellers account past this limit and something else.

I’m not very strong in PHP coding and I need to resolve this ASAP.