Unexpected weight loss 😔

I am 16 and 5 so far I’ve lost a total of 20 pounds since my first appointment at 6 weeks.. my OB said this is concerning and if I lost 4 more before my next appointment I may face hospital admission.. I was over weight before hand so at first he was not too concerned but now that I’ve almost lost 25 it’s an issue.. I have no idea what to do I’m eating but I really can’t eat that much as I still have morning sickness.. and my stomach is just not as big.. I know that I’m supposed to gain weight at least 15lbs throughout the whole thing but I’m

Not sure how to do that seeing how I’m actually eating currently but losing weight..