Well done for sticking with it, don't be discouraged by weight loss. You've been given lots of great advice. Have you got an express machine? I have heard of something called dessert feeding. Where you express after you have fed baby then use that to top give them as a top up after next feed. It helps increase supply and apparently is easier for baby, helping weight gain. Perhaps ABA would be able to tell you more about this if you feel it would be of benefit as it was someone from ABA who told me.

Thinking of you, you're doing a great job!