Lag in upload to website?

I have a very basic level of understanding when it comes to websites.
Have enough knowledge to get me through dreamweaver and produce a pretty simple site.

The problem:
Occurs when i upload updated web pages to my site that already exsist.
For instance if i update some text or change an image on any given page and upload the new page under the same name.
When i do so the page won't immediatly show and on some occasions takes up to a week to change from the older version, this has since got a bit worse and now it decides to show me the old page sometimes on some computers, and the new on other occasions. It also differs accross the two variations of my domain name, i,e: and

Does anyone have any ideas why this occurs and what i can do to ensure the pages are availible quicker and more consistantly?

Thanks for all your time in advance.
First source: Your web server probably caches pages in memory, so that if you request the same page again, it won't be forced to read it from the disk. You need to empty the cache, or "flush cache" as it mostly called. Depending on which platform and server you are using, this is done in different ways.

Solution: Talk to the administrator of the server to find out how it is done on yours.

Second source: Web browsers also store local copies of web pages you've visited in a special folder, also called a cache.

Solution: Check the settings for your browser, and you will find a setting for cache size, and also a button you can click to empty the cache, to allow for retreival of the updated pages.

Normally, you shouldn't have to do any of this, since a well behaved server should check to see if there is a newer version of the document than the one residing in the cache, and so should your browser. This doesn't always happen, depending on server version and configuration, and browser application and version, respectively.
I thought it might have something to do with my cache so i have emptied it almost on a daily basis and have now found software to combat it.
I guess the problem must lie at my server, i'll get in touch with them.
Thanks for your help.
I have been in touch with my administrator and it looks like it has something to do with my uni network. The pages view fine out of my uni network. Noting can be done as far as i'm aware?
If you browser is not caching, and the server is not caching, then you must have a proxy/caching server in between.

You can try coding all of your pages with the pragma no-cache meta tag (Google to get details) to see if that keeps the proxy/caching server from keeping the cache. Not all proxy/caching servers honor these meta tags, so you might need to experiment with different solutions.

Some of the solutions require altering the HTTP Headers that the Web servers send. That would mean you'd again need to work with the Web server admin (unless you are using a scripting language like PHP or ASP that can change these headers themselves.)