My daughter is 5 months old and is breastfed. About three weeks ago she had two days of formula for the first time and hasn't had any since. She may have pooped twice since then. The only thing that was different about the poop was that it was a little darker. She has not pooped in over a week. Everything else seems normal. She doesn't seem uncomfortable and I haven't had any diet changes. What should I do to help?