Constipation and gas

My one month old little girl has really strong, loud, awful smelling gas. And she hasn’t pooped in 3 days. I’m using gripe water and nothing. She is breastfeeding with some supplementation. I switched formula to similac because I ran out of enfamil which is what I was using. but I think when I switched it kinda help cause this problem so I’m switching back. How long can that stay in her system? I’m doing the bicycle and rubbing tummy too. I just want her to feel better (and smell better)