Website very slow

Hi! We’ve changed our theme a couple of weeks ago, from Mystile to Fitshop. Our server is bluehost, and when we were running on Mystile the site was a bit slow. But right now is a complete despair, any page spends a century to load.
Could it be related to the theme? Or is somenthing wrong in the server.
Anyboy knows what to do?
Thanks in advance