R.M.
I always switched back and forth between fruits that would constipate and those that caused loose stools. Once the food has been introduced with the 4 day rule, I would give him apples or bananas one day and the next give him peaches or something. If i noticed the poop getting too firm I'd stay away from the constipators, and if it got too soft, I'd give him more of them. Prunes always worked really well, I usually only gave half a jar and it would do the trick.
Here is a website article that talks about feeding a baby with diarrhea. The top list that "helps" are the ones that can cause constipation. The bottom list to "avoid" will help get rid of constipation. Once he is regular, if you rotate them around and not feed too much of one kind in a day, he should stay pretty regular. A trick I used to remember the main ones is that if they start with a P, they are foods that will make them poop. (pears, peaches, plums, prunes.) Made it easy to remember some quickly when I needed to give him something to keep from getting more uncomfortable. The whole website is great and really helpful. Hope it helps you!
http://www.homemade-baby-food-recipes.com/feeding-a-baby-...
Also, I think I was doing 2 meals a day about this time, but you don't have to. Just give him more solids as he seems more hungry. I would do a fruit for breakfast and a veggie for lunch or dinner. And I would give him one thing I had already introduced, and for the other meal I would be introducing something new. But I would stop introducing new things until his constipation is better.