Baby not gaining weight

I’m looking to hear from other parents that have overcome weight gain/feeding problems, as I’m currently feeling so defeated.

My LO was born by c-section weighing in the 96%. Our BF journey was amazing for the first 4 weeks. Then I suddenly dropped a ton of weight and likely lost my milk supply but didn’t really realize. Over a 3 week period, my baby lost 1oz of weight :(.

Our family doc said to start offering some formula after feeds. She devoured 3 bottles of enfamil neuro pro and got a worse and worse full-body rash with each one. We then switched to Nutramigen, which she LOATHED entirely (even mixed with ebm). So we switched to RTF Alimentum and she will ‘tolerate’ it if she’s starving enough before breastfeeding, but still only takes about 2.5oz by bottle before she gets cranky and wants to go back to sleep. She will only latch onto the breast for a couple minutes, so I know she’s not getting much there either. I’ve also tried European goat milk formula in desperation and now I’m waiting on an order of Hipp pre HA in hopes that she likes the taste better.

We were referred to Pediatric Urgent Care due to poor weight gain. She’s now 11 weeks old and in the 23rd %ile (I know that doesn’t matter but she keeps dropping rather than maintaining her curve). They diagnosed her with a heart murmur and an LC diagnosed her with a tongue tie.

I’ve been on fenugreek and blessed thistle for ~2 weeks with some increase in supply and I just started on Domperidone. The breastfeeding centre wants me to increase my supply before we release her tongue tie so that she does not get angry with low milk flow while she’s recovering.

I’m just constantly feeling like I’m failing my poor baby. I desperately want her to be healthy and gain weight, but I’m at a loss.

I guess I’m just seeking consolation from someone else that has been through a similar experience with a positive outcome or any advice.