I have just introduced formula to my once exclusively breastfed 5 month old. I give her about 30 cc of formula in addition to breastmilk at almost every feed. For the past day, she hasn't had a bowel movement (which is unusual for her) and she seems to be trying to strain (uncomfortable). I am wondering if there is anything I can do about this? I am afraid to introduce more formula to her since she is having this reaction to such little amours? Any advice would be greatly appreciated.