What a worrying time for you

First, is your nurse a lactation consultant? It woudl be best to get advice from one if she isn't. Or definitely call the ABA - they can give you advice also and help you find an LC in your area if can't.

Lots of wet & pooey nappies and growth sounds good - so you're obviously not far off here. The one-off "test weigh" can be very misleading as babies tend to take differing amounts of milk at different times. You might get a big gain or a very small one, but it doesn't necessarily reflect your supply.

How many feeds is he having in 24 hours? On the face of it, it seems there's a reasonable amount of milk going in so it's worth talking with an LC to get at any underlying problems here. Is it a supply problem? Is it a feeding problem? Is there someone else going on stopping him gaining weight? And so on. Sometimes just adding supplements isn't the answer.

Anyway, as I said, it doesn't sound like you're far off here. He's not starving, ok? He's just not gaining weight like you would want