Problem with pages not loading

I got my MacBook Pro about two months ago and just in the past couple of weeks I've been having a problem with random pages not loading. I get an error message saying that it can't load the page because my mac isn't connected to the internet or that it can't find the server. I check my internet connection and it's fine. I even turned my old computer on and it connected fine. I was using Safari but this started happening more often so I switched to firefox but it's happening on firefox now :/ If I try to refresh the page it comes up with the same error but if I wait for about 15 minutes and try to refresh the page it loads and if I'm in firefox and it happens and I open safari and go to the same page it will load but come up with the error message after a little while. I've tried emptying the cache but it didn't do anything. Does anyone have any advice?