Can dairy = Constipation ?

Raf doesnt drink a huge amount of milk but does get yogurt and cheese in his diet .Over the last few days he has been doing very hard ..rock hard poops which have made him bleed.I am worried about it being to much cheese? He drinks an adequate amount of fluid a day and eats a varied diet so I cant figure out what might be causing it.I am adding prunes to his brekky and afternoon snack in the hopes of softening everything up any ideas?