Upset Baby Tummy

Our baby boy will be 20 weeks tomorrow and is breastfed. For the past two days his tummy has been upset. He has poop in almost every diaper. Now his poor behind is red and irritated. I'm treating it with Boudreaux's Butt Paste and A&D ointment. He isn't acting like he is sick or in pain. I'm not sure if it caused by something I ate or if I gave him a bug. My stomach hasn't been well for the past few days either. Is there anything I can give him for his upset tummy?