Lag / Slow Site

I have been searching through the forums for a while now and there are alot of posts with similar problems, but I’m fairly new to WordPress and I couldn’t really understand any of the solutions given.

Basically I’ve recently set up my site and all has been fine until I made a new post, and then it started going incredibly laggy. It sometimes takes 40 seconds to load the admin page, and the main site. I have disabled all plugins, deleted the ‘ping’ address in the write options and it’s still as bad.

I’d really appreciate any help I can get because it seems like a common problem, but I’ve missed something silly >_<