T.B,
I am going through the same thing but my son is 2 years old. My son is a picky eater so I have to hide the prunes in his food, but sometimes he notices and won't eat. He likes Yogurt and some of the yogurt we give him from Trader Joe's has Tapioca starch in them and that works for my son. But I have it where he is now going #2 every day 1 time a day. he was holding it for 2 days and it's still hurting him when he goes and now at the age he is, he knows he can hold it but when he does go it does hurt. I am trying to give him stuff to soften it for him. I have tried "Benifiber" in his milk, tasteless fiber. That seems to help him, I would actually check with his Ped to make sure, but if you are trying most of the things the Dr will say "Water, Juice" and also massage works.. Warm baths' too. I wouldn't recommend laxitive or sticking anything in his rectum to make him go. I read up about it and they say if they haven't gone #2 in 4 days is when to worry.. But juice and water work best and prunes, pears, veggies..
Also every diaper change I put Vaseline down there to help ease out for him too.
Good luck