My 7 mth old has infrequent bms, often 7-9 days and when she goes it's huge & explosive! she is a fussy baby and hates to bend to sit. need i worry?

Explosive stools: You don't mention whether you are breast or bottle feeding. From your description i'm assuming you are breast feeding. Breast fed babies may have a solo with each feeding, they may have one once or twice a day or they may go as long as a week to ten days without having one. Because of the delay these stools maybe explosive in nature.

Pediatrics eval: Though this is possibly normal, it would help to find out if your baby has food intolerances, decreased innervation to the colon or intestines, a dilated colon, or another structural reason for slow transit. Check with a local osteopathic physician who specializes in pediatric manipulation if your pediatrician does not find any reason for the infrequency of bowel movements.