How do I speed up my wordpress site?

Hi There, would really appreciate some help on this - any help.

Recently my wordpress multisite network was migrated from godaddy to bluehost by the bluehost professionals.

the main site sold-magazine.com.au has been 3x slower ever since. And by slower i mean slower loading times -- and heaps slower in the dashboard. Trying to add a post or change a menu is a nightmare. I might as well go make a cup of coffee after clicking "add new post". Blue host say its a problem with my site. My site has around 800 posts and 600 images. I don't have a feel for whether thats large or not.

I'm running the latest versions of wordpress, not many plugins, and a theme called sahifa, which is a theme that I purchased on themeforest (their most popular wordpress theme ever).

Blue host say I'm being throttled because I am using too many resources, but they cannot tell me what or how. I'm not sure how that can be, the site gets around 200 visitors per day, its just to read articles (I'd like to add buddy press but not until I can get the performance better). And as I said before it was faster on godaddy (when the site was up in the first place!)

I don't want to have to move hosts again, but I need some good advice the finger pointing and the not knowing what or why is driving me crazy!!!