Is it okay that my 3 week old didnt poop today? Formula fed only.

Okay so she normally has normal poop every day. But lately she started eating like a lot more than she used to. She will easily kill 4 oz every 4 hours. She pooped yesterday morning but none for the rest of the day or today. She has CLEARLY been trying to poop but so far nothing and its making her fussy. If she doesnt poop by tomorrow morning I will have to call her pediatrician first thing monday of course since they arent open on weekends. What do you guys think? Should i switch formulas? She was doing great since birth on this formula but idk now???