If your baby is not showing any signs of discomfort then I would stop worrying so much. Breastfed babies can go for a week quite comfortably without needing to poo. kellymom.com is a great website for all queries with breastfeeding too if you want to have a look.

To the solids baby...my first had the same problem with constipation - I finally worked out that it was the rice cereal (der!) but not before she was just in agony when she had to poo...prune juice helped alot as did peaches...best of luck...