Weight gaining issue

Delilah

My LO was born at 37 weeks via C-section, 5lbs 15oz. We are now at week 5 and have not gotten back to birth weight. This week she hit 5lbs 12oz on Monday and we were all so excited for her but has since plateaued and hasn’t gained anything as of today. She is eating every 1.5-2 hours with a combination of BF and bottle feeding with pumped milk and formula. We’ve been fortifying her bottles to 24 calories but all at no avail. We average 6-8 wet diapers a day but barely one poop a week. She seems to have serious reflux issues taking a bottle (generally spits up the entire thing or at least 1 ounce). I keep her up right for 30-45 minutes after bottles but she still ends up losing a good bit when she is laid down after. We’ve been going in for weekly weight checks and are now being referred to GI. Has anyone else experienced this? I need some encouragement. My first born was born at 31 weeks, 5lbs 4oz and never had a problem gaining. I’ve been told 37 weekers end up having the most issues and the highest rate of rehospitalization? She hasn’t even entered the 1st percentile on her growth chart. I’m definitely one stressed mama!