Baby with a weak suck

So I just got out the hospital with my 6 week old son because he was slightly malnourished and below the 1st percentile for weight. We found out he has a weak suck due to a recessed jaw, weak suck, and high arched palate. It's causing sleep apnea, oxygen desaturation (fancy word for not getting enough oxygen) and an inability to feed correctly. He was over exerting himself trying to feed and burning more calories than he was taking in. He's now on oxygen while he sleeps and I'm having to fortify my breastmilk with formula. Does anyone have any experience with this or any advice? We were in the hospital for a week and given a bunch of tips to feed him, but we're still having trouble with feeds, feedings are lasting 45 minutes or more usually. He's still having lots of trouble and doesn't seem to be getting any better at sucking. I feel so bad for my little guy but I'm so exhausted