Hm. Can you give an idea of what's going into your broth? Like what kinds of bones, or any veggies if you add them? Also, have you been getting the bones from the same source? Maybe you want to switch up your supplier.
I'm reluctant to pin that as the problem, though, because the only place I can get a steady supply of broth-appropriate bones that aren't exorbitantly priced (Whole Foods charges 7 bucks a pound! For BONES!) is the HEB, basically the Texas version of Food Lion, and they're certainly not from organic or grassfed animals. I drink a cup, sometimes two cups, of bone broth a day and I've never had the problem you describe.