Baby constipated what to do?

My baby has not pooped. She pooped last time on Thursday morning and has not pooped since then and today is Saturday morning. Her last poop was not hard and was normal and yellow seedy.

She is 3 week 3 days old and breast fed in day time and formula fed at night from birth. She cries at night and stretches her legs and passes gas. She is passing gas at day time also. She is getting wet diapers and feeding normally after every few hours. She does burps after feedings. Im assuming it could be gas or constipation. Since she is passing gas so may be its constipation. What should i do?

Please help