3 week old not pooping

Kind of long sorry lol - My baby usually poops several times a day. She is breastfed and I give her formula 1-2 times a day. She’s not had any formula since Sunday and coincidentally, the last time her bowel movements were “normal” was Sunday. She didn’t poop until yesterday afternoon. It was one time, large amount, and looked like breastfed baby poop. Hasn’t gone since! She’s been fussier then usual, I can feel her belly bubbling with gas and she strains a bit before she passes gas. She doesn’t arch her back or anything but her cries are so loud and she has little tears and her face gets red it makes me so sad! She slept pretty normally last night but yesterday during the day she didn’t sleep long and the only thing I knew I could do was offer her a feeding which seemed to at least pacify her. My pediatrician said it was normal for her to go a while without a bowel movement but now I feel like she’s in pain and was just wondering what else I can do for her lol