Sometimes you get issues with your speed at different times. Probably the contention issue.

Here is a site, as long as you're not on cable, that may help.

link

Click on the top link called user tools

On the left hand side click on Exchange Status. In the new window that appears type your 'phone number, unless you know your exchanges' code, then you can check if what state the broadband is. In the list that shows click the here link in the sentences and not the ? to the right.

If you get Amber for Virtual Paths then your line is over subscribed with other customers who have priority over yourselves who are moderate users possibly. Gamers, Skype users, etc, have priority even though you pay equally for your broadband connection.