I buy a very dense multi-grain bread from Wegman's. It's my favorite bread of all time. I can keep it for weeks in the refrigerator without any mold appearing. Sometimes it comes up sooner, if I've left the loaf out for a few days after buying it. I just cut off the mold and eat it. NEVER had a digestive problem from it. The mold can't survive the harsh acidic environment of the stomach, is what I'm guessing.
What I recommend you do if you don't go through your bread very quickly, is to take half of the loaf, seal it up in a plastic bag and put it in the freezer. Honestly, if you take frozen bread, zap it in the microwave for like 15 second, then toast it, you'll be hard pressed to tell the difference from relatively fresh bread.
And in the future, always check the expiration date. I do this all the time and usually I can find stuff with a later expiration date in the back. Sometimes by as much as a week or two.