Mobile width changes after load

I had a problem recently with a very thin body when accessed via mobile device. I received help here and everything worked well for a little while.

Now, my site starts at the right (full) width when accessed via mobile device. After it loads fully, however, it shrinks a bit. It’s not as bad as before, but it’s still much harder to read than when the body is at full-width.

My site is The Stylist Quo and I’m using a child theme of Twenty Twelve.

Could this be a banner ad issue? Is there some CSS I can use to fix this? Help please!