Hi OP, I think it's totally understandable that you've got these concerns, especially since you're someone who has worked very hard to lose weight in the past. The truth is, everyone's body is different and deals with pregnancy differently, so the main thing to focus on is that you're eating the recommended amount of food. For someone starting pregnancy at a healthy weight, the recommended weight gain is between 25 and 35 pounds.
I was so worried in my last pregnancy because I gained about 10lbs in the first trimester and they say you should be gaining no more than 5 with most people only gaining 2-3. In the end, I gained just over 2stone (well within the recommended amount) because for some reason my weight gain stopped at 34 weeks.
With regards to the weight loss, I only lost about 9.5 lbs in hospital, but DD was only 6lbs. I think most people lose more than that. The weight steadily came off and I was back to my weight in around 8 weeks. I didn't diet as such but I breastfed and made sure I didn't over indulge. Just like I did in pregnancy.
Hope this helps. It's worth noting that some people gain a lot of water weight which comes off almost straight away once the baby is born so don't get too hung up on what the scales say 😃 x