I'm sure this comes up all the time, so I apologize for the repetition. I could use some individual help though please. This is pretty long bc I need to give his full background. Thanks!!
Background: My son was born at 36 weeks with a heart defect and Down syndrome. He was in the hospital for 3 weeks and we have been home for about 5 days. He was too sleepy to eat and was tube fed breast milk. At 2.5 weeks he woke up enough to take his bottles and we were discharged soon thereafter. I met frequently with a LC and he was able to latch but we had to focus on numbers and couldn't use BFing for his feeds. He has had swallow studies and worked frequently with an OT and has no physical limitations to eating.
We still have to make sure he gets enough food. He is very small and still isn't back to birth weight (5 lbs). He has open heart surgery in his not too distant future and we need as much weight gain as possible. We are not fortifying because he battled a stomach infection in the hospital which we suspect was started from irritation from his fortifier. If he does not gain at his next weight check we will talk about fortifying his milk. I really want to avoid this.
I introduce him to the breast a few times a day but it just makes him mad. He will latch but then start yelling out of hunger and refuse to try again. I also try with a shield. It was successful the first time but he won't even latch to it now. I speak to my LC and she is helpful, but just says to give it time. She has taught me how to do weighted feeds but I don't want to encourage my neuroticism by purchasing a scale.

Mainly I am just looking for some tips, tricks or encouraging words. I really hate pumping and would love for him to BF a couple times a day. I just have no idea how to get him to take it. Also I EBF my first child for 10 months so I have some experience with the process.
Tl;dr - how do I get my NICU and medically fragile baby to take the breast, and encourage weight gain?
Re: Transitioning from bottle to breast (long)
Me-36, Unexplained Infertility, DH-35, all clear
Clomid 50mg 12/2011 = BFN
Clomid 100mg 1/2012 = BFN, with Cyst
IVF #1 Lupron/Menopur/Gonal-f/HCG Trigger
ER 4/19/12 = 11 retrieved, 6 fertilized,
ET 4/22/12 = 2 transfered (day 3), remaining 3 weren't good enough to freeze
Beta 5/3 = BFP, 87 Beta #2 5/7 560.9 Beta #3 5/9 1376.5 First u/s One Baby, 125bpm!
Second u/s, 176bmp! Kicked over to the OB by the RE at 8w. Team Green!!
We had similar issues (born at 36 weeks, less than 5 pounds) and dealt with tongue/lip tie, never did get him to the breast I just EP but from I've seen, we're the exception, most people who are willing to put in the effort can get baby back to the breast.
Make sure you are using a slow flow nipple, the slowest you can find. Playtex actually makes a preemie nipple that is really slow. Agree with PP on hand expressing or pumping a few minutes to get your let down started, that way he gets an instant reward when he gets on (though, I have found that wetness can make latching a slippery business so there's a trade off there). You could also try a supplemental nursing system but I would only do so under care of an LC as they can be tricky.
Stick with it and give him lots of skin to skin time, that will help calm him and help your milk production too. Some people have luck BFing in the tub (have someone help you of course) because you're both warm and relaxed and having skin to skin time.
Good luck and I hope his surgery goes well!
PS I've also heard that DS babies can have high or bubble palettes and that can give them a shallow latch, has he been evaluated for that? It's not a deal breaker, just something that can make it harder to latch properly. If he was latching too shallow, you usually end up with sore/misshapen nipples.
BFP#1 1/31/12, EDD 10/6/12 Harrison Gray born sleeping @ 18w6d. You changed our lives little guy.
BFP#2 EDD 10/29/13, C/P 2/25/13, Bye little Ish, we barely got to know you.
BFP#3 EDD 12/21/13, Baby Boots born 11/23/13 My rainbow baby!
January PAL Siggy Challenge: Good Advice