No bowel movement in eight days

My son has been having bowel movements every 3 to 6 days for the past month and a half.  His doctor said it's normal for a breast fed baby to go 5 to 7 days without a bm.  Today is hi eighth day without a bm and now the doctor wants to do an x-ray of his stomach.  I'm just wondering if anyone else has gone through this and if so what was the outcome?  His doctor said she has never heard of a breastfed baby going this long with such a weird bm pattern so I am beginning to get a little worried.  Any suggestions?