i'm a little surprised that your pediatrician just recommended a suppository and prunes for a baby who hasn't had a bowel movement for 4 days. keep trying the suppositories- it will take them a while to soften stool that hard.
you might need to very gently insert a gloved and lubricated finger just a little and massage the impacted poop to help it break up and get out. be very careful, but you can actually physically scoop it out.
which is what i would have hoped would happen in the doctor's office. another good option would be to call them back and ask them to help do just that.
poor little guy. if he's in serious pain you may have to take him to Urgent Care if your pediatrician won't help him.
khairete
S.