since you can access htaccess, check for these, and if not there, add them:
## EXPIRES CACHING ##
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/jpg "access plus 6 months"
ExpiresByType image/jpeg "access plus 6 months"
ExpiresByType image/gif "access plus 6 months"
ExpiresByType image/png "access plus 6 months"
ExpiresByType text/css "access plus 6 months"
ExpiresByType application/javascript "access plus 6 months"
ExpiresByType text/javascript "access plus 6 months"
ExpiresByType text/x-javascript "access plus 6 months"
ExpiresByType application/x-shockwave-flash "access plus 6 months"
ExpiresByType image/ico "access plus 1 year"
ExpiresByType image/x-icon "access plus 1 year"
ExpiresDefault "access plus 6 months"
ExpiresByType application/x-httpd-php A0
ExpiresByType application/x-python-code A0
ExpiresByType text/html A0
</IfModule>
## EXPIRES CACHING ##
and the headers as well:
<ifModule mod_headers.c>
<filesMatch "\\.(ico|pdf|flv|jpg|jpeg|png|gif)$">
Header set Cache-Control "max-age=15778800, public"
</filesMatch>
<filesMatch "\\.(css)$">
Header set Cache-Control "max-age=15778800, public"
</filesMatch>
<filesMatch "\\.(js)$">
Header set Cache-Control "max-age=15778800, private"
</filesMatch>
<filesMatch "\\.(xml|txt)$">
Header set Cache-Control "max-age=15778800, public, must-revalidate"
</filesMatch>
<filesMatch "\\.(html|htm|php)$">
Header set Cache-Control "max-age=1, private, must-revalidate"
</filesMatch>
</ifModule>
notice that in both directives the php/html/htm is set to expiring the cache either immediately or at access +one second... If you don't have the rest of the directives, give them a shot. you'll like what it does for you most likely. caveat: these aren't a good idea UNLESS you rarely change/alter your files...
that 'should' take care of your problem, which is the output of php (html) is being held on to for too long... even 60 seconds can be too much for a forum if people are waiting around for a response, and not seeing one within a minute (because the cache let it live that long).