Problem with Macbook accessing certain web pages

Hi, I've recently started having problems with my Macbook (april 2009 model); for some reason its been struggling to open certain webpages and just times out. I'm mainly having trouble with ebay, facebook and hotmail. But whats strange with ebay is that it opens pages fine when just searching for items but when I want to access the 'my ebay' pages (my account details etc..) it has frequently been timing out. Then at other times it works fine and I can access everything.

I also have a pc that runs off the same wireless router and that seems to work fine all of the time. I've tried emptying the cache and deleting the internet history on the macbook but this hasn't done anything.

Anyone got any ideas?

Cheers