Desperately need advice

Hi guys, I’m hoping y’all can help! Pre-pregnancy I was 210lbs and now at 31 weeks I’m 169lbs. My baby is measuring great and seems perfectly healthy, but I’m literally struggling. My OB is concerned and really wants me to start gaining some weight - I’m trying so hard but literally cannot eat more than a few bites without feeling so full and nauseated. Do you guys have any advice for gaining a little weight??? Background: I had gastric bypass in 2021 so my stomach is very small. At 26 weeks pregnant, I was admitted into the hospital with severe abdominal pain (something I had been dealing with on and off for 2 years) and found out I needed emergency surgery. I had an internal hernia (a complication from my weight loss surgery) with intestinal strangulation and sepsis. I was told baby and I would have died if I had waited another 2 hours. So I’ve been recovering from that and eating has been difficult bc my insides are literally healing and learning to function again. Sorry this is so long - I’m just at a loss. I want to do what’s best for my baby and I know that’s making sure I’m healthy.