Bfed bubs can go up to 10 days without a poo with no problem, (and mine often have!). But I would think they would go more often with solids in the mix. Banana can cause constipation, so I wouldn't give anymore of that for a while. Potato also. But I wouldn't worry yet, just cut out the problem foods, and make sure he drinks plenty. I wouldn't give much in the way of solids, in the first couple of weeks a teaspoon a day is usually enough. Also warm water can help as warmth relaxes the bowels. People will tell you brown sugar in hot water works, scientifically there is no reason why brown sugar would work, so it's probably the heat that has really helped. Give it a couple of days.