Our 11 week old son just went 20 days without a BM! He is exclusively breastfed and had regular BMs before this. He was eating on his normal schedule and had the same amount of wet diapers. His temperament was great so we didn't think he was in pain or constipated. We called the Pediatrition's office at 7 days and 14 days. They told us the primary indicator is temperament - so if he was happy and having regular wet diapers he was probably fine. After the 14 day call they also encouraged us to give him baths with baking soda as it is supposed to relax him and encourage the BM.
This morning he just went with no encouragement from us. We had called again today worried that 20 days was too long and they encouraged us to try the liquid infant suppository and schedule an appointment with our Dr - fortunately he went before we had to go through with either.
Remember it is very important for Mom to stay hydrated too so the baby is getting the best quality breast milk possible.
We have never been so happy to see poop :)