WordPress site really slow to open

Hi there, I’ve been running the mentioned site for a while now and all has been fine. Recently it’s started to take a very long time to open up – around 6 seconds for the opening page to pop up. We can’t see any obvious explanation. The site also seems to be using a lot of resources and space and we’re regularly getting messages from our server supplier saying that our “resource limit has been reached in the past 24 hours.” Can anyone help? Kind regards JOSEPH KELLY

The page I need help with: [log in to see the link]