My suggestion is to put a little baby prune juice(diluted) in his cereal or formula/breast milk. Try that a couple of times a day..... for a couple of days, and see if it helps. That's what I did with mine if they ever got that way and it worked. If he hasn't gone within three days I would call his doctor and see what kind of laxative would be safe to give him. I think it's normal for this to happen, b/c his body is getting used to solids(his poop will be different than before). I wouldn't be alarmed unless he seems to be in pain, or doesn't go after the third day. Keep us posted
Also Krista is right try peaches or pears instead of applesauce or bananas! Hope this helps you!