Hi,
It's normal that the new items don't appear if you try again with the same URLs as they get cached. Change the parameter to something else like ?test2 or test3, etc and you'll get the new data displayed.
Unfortunately, I can't tell you what is caching the pages on your website/web server as I don't know. That's something you, your system administrator or your hosting company should know. If it's not the Joomla caching options/plugin then it's something else. Maybe something directly on the web server that cannot be changed in the backend of your website.