12 day old, pooping pebbles? bottle fed, really struggles and strains to poop? what can i do?, should i be concerned?

Not to worry: Child is little different from other bottle babies. The pebbles represent hard stool. This may indicate the child may need more water in the diet. If not blood but straining I would not worry too much. You need to talk to the pediatrician for suggestions to increase water and any need to use a stool softener. follow the docs advice, Congratulations

Change formula: It sounds like constipation, which may be from the formula she is taking. I would recommend trying a different formula for a few days to see if it helps, then stay with it. No medicine at this time.

Change formula: If your baby is otherwise well, this could be a simple intolerance to the formula. You could talk to your pediatrician about changing to a more tolerable formula. You also want to check and make sure that the baby is gaining weight appropriately.

Baby constipation: It is not unusual for bottle fed babies to have problems with their bowel movements. Formula is not a perfect reproduction of human breast milk. You should take your baby to see the baby's usual healthcare provider. I recommend that you take a soiled diaper so that the provider can actually see the pebbles. The doctor may be able to recommend a different formula or other intervention.