Congrats on the surprise!
I imagine a lot of us came into the world that way, I know I did.
When are you due? Mine is December 19th.
Without boring you with too much of a backstory, I'd been working extra, extra hard to lose weight after losing my first pregnancy to a miscarriage early last year, in hopes of carrying a healthy baby full-term. I'd managed to lose over 60 pounds by the time I'd found out I was pregnant (150 down from my highest!). And as much as I want a baby, I felt like I'd been stopped in my tracks. I was on such a roll, at my lowest weight since junior high(!), and only 12 pounds away from a super major goal of only being "overweight" as opposed to "obese" for the very first time in my adult life! I'm both excited and frustrated, lol. Part of me is afraid I'll have a hard time starting up again once the baby is here, and I'm still cringing over the watching the scale go up, even only slightly, even though it's what my doctor wants to see. I've been working so hard for over a year to lose, and I've had to change my mindset about most everything.
Basically, you should go over your weight concerns with your doctor; it's something I brought up with mine immediately, asking specifically how much she wants me to gain. Also ask to get tested for gestational diabetes right away, as your risks are higher with your weight and it's best to take care of things now if there are any issues. My doctor hadn't actually planned on testing me until the second trimester, which is the norm for someone at an average weight, but I'm glad I got those worries out of the way since I was extra high-risk for it, also given my blood sugar history.
Just keep eating healthy (you only need about 300 extra calories a day) and get plenty of low-impact exercise in to ensure you're strong and flexible for the delivery. I can't really give much more advice though; I'm only 15 weeks along myself and everything is very new to me still! I'm just hoping that I don't gain too much and that it won't be an issue to get back on track once the baby's here (I do plan on breastfeeding if possible so that extends things even further). What I'm doing for now is logging my food in a weekly planner, like I've already been doing for the past year, to ensure that I'm staying mindful about eating healthy meals. I'm still watching my portions and concentrating on veggies, lean meats, cheese, greek yogurt, healthy fats, fruit, whole grains, and I'm continuing to avoid added sugar and overly processed crap; I just make sure I eat a little extra. I'm hoping that it'll help ensure not only a healthy pregnancy, but that it can help me transition back into weight loss mode so I can reach my goal in the next couple of years and so my baby can grow up with an active, healthy mom, and not one that sits on the sidelines and just watches everything.
Good luck to you!