New born not pooping!?

Hello Everyone.

My brother is here visiting. With my 3 wk old niece. She has had two HUGE bowel movements in 6 days (like had to have 3 diapers ready cause it wouldn't stop kind of poop). But she hasn't pooped in 2 days. We've tried the gas drops. Belly time. Bath time. Leg movements. Rubbing her belly. And while it helps relieve gas, she isn't pooping. She's not being over fed. 4oz (every 2 to 3 hrs) and she sometimes doesn't eat it all because she's so gassy. Mom and my bro both told the doc the formula was bad on her. But doc said theyre over feeding. But I've watched and they are not. Mom went and got a different formula (reguline Enfamil) that seems to be helping her get her gas out way better.

Ideas? They live in MI. And are visiting here in TN. Theyre cutting their vacay short and leaving tomorrow if she doesn't poop today.

Tips??