My Site speed has dropped like a stone for some reason

Hi there - I spoke to an agent earlier as my site performance has dropped dramatically. There a lot of items that need compressing apparently that have a reference to FB in them and he said that it was likely a new plugin. I've been through all the recent plugins that have been added in the last 3 months and nothing makes a difference when turned off. I really need further insight into what this might be now I've eliminated plugins. Thanks