Iron supplements causing bad breath?

I'm 30 weeks pregnant and for the last few weeks I have had horrible breath. I've never experienced this before. I brush my teeth, floss and use mouthwash twice a day but suddenly this is not enough. I have no idea what's going on. Could it be my iron supplements causing this? I have however been taking them since the beginning of my pregnancy and this problem has just come up. I'm not sure what else it could be. I don't have any problems with my teeth, stomach or anything else.