Hello, welcome, and congrats on baby #2 and finishing your nursing program!
When did you start gaining weight last pregnancy? It can take quite a long time to stabilize and then start gaining. I too lost 25 lbs by 12 weeks (and I was fairly tall/slim before), and then didn't start gaining any back until after 16 weeks. Even at that, it was very slow, regular gaining until the last couple weeks, then I gained like 5-7 pounds all at once. I'm still about 10 pounds below pre-pregnancy weight at 26 weeks. Last pregnancy followed about the same pattern for me, and I did end up gaining a pretty good amount of weight in the last 12 weeks.
If you're able to drink a few (like 2-4) ensure with extra protein per day, you'll get the nutrition and calories you and baby need. I drank these, ice cold, for weeks. Don't chug them, just sip on them throughout the day. If you are still struggling with not gaining weight back any weight by 18-20 weeks, then maybe your doc can recommend TPN or and NG tube, but hopefully you won't need that? I call ensure "TPN in a bottle". Food by mouth is always the better option if you can handle it that way, and if you're eating now, I'm sure you'll be fine by the time your baby starts growing more.
DD1 born Jan 29, 2010. Mod-Severe HG. Started treatment at 5 weeks. c-section (breech)
DD2 born July 23, 2012. Severe HG started treatment at 4 weeks until birth. VBAC!