website running very very slow..

My wordpress site https://www.melissademing.com/
is running very slow all of a sudden.It clocks and then errors out on internal server error 500.I do have w3 super cache plugin installed.I ran firebug yslow test ,as well as https://sitecheck.sucuri.net and both of them listed
https://dtym7iokkjlif.cloudfront.net/dough/1.0/recipe.js
i do not understand where it is coming from .It looks like virus attack to me.How do i remove it?Thanks so much.