How does gaining weight work?

Ta
Pardon my strange question but FTM here and my adoptive mom was never pregnant so I can't ask her...how does weight gain occur during pregnancy? Will my appetite eventually increase so I will want to eat more? Or should I start force feeding myself? I'm almost 14w and am still down 6lbs from pre pregnancy weight. I really have no idea how I'm supposed to pack on the 25-30lbs that the doctor wants me to put on. I've been pushing myself to take in 2400-2900 cals/day but it's work 😕 I walk daily, swim for relaxation and we hike once a week = trying to stay semi-active but it's nothing strenuous. If possible, I'll like the weight gain to be gradual as I think that's healthier?
Sorry if my question seems silly but I don't know how this works and my only concern is that my growing baby gets the nutrients and calories that he needs. Thx!
UPDATE: Thank you so much for your comments & input! Am 17w and still losing weight (maybe this baby is really a giant human shaped tapeworm). Saw OB this week and since I've lost another 5lbs since my last appointment, he wants to see me in 2 weeks time. FTM and we've endured 3MCs in a row so I will do whatever it takes for baby to be healthy. Guess I should start looking up the Sumo Diet 😂...