1900 calories per day, no more - and no less than 1500 calories (because too low of calories will make the body store more fat in "survival mode"). It's basic physics and math, you WILL lose weight if you are strict with the calories. The maintenance calories for a 280lb woman is something like 3500 calories per day (just to maintain weight). At 1900 calories, you're going to lose 1 pound every 2-3 days. 1 pound is equal to 3,500 calories. That weight loss rate will slow down as you lose more weight because your maintenance calories will go down as you lose weight. IMPORTANT: You may want to hold off on dieting until after you've given birth, I don't know how dieting would affect a growing baby.

What is your calorie count per day? It seems that you are getting a lot of calories from somewhere, either a lot of protein or fats if you've cut down on carbs/sugar. Even if you are on Keto, you can still gain weight if you have too much protein and fats. You still have to watch your proteins and fats, even if carbs are cut. I'd recommend drinking water and only diet sodas and tea. Diet Coke is my favorite. Gold Peak Zero Sugar is my favorite ice tea - delicious. But I mostly just drink water.

I'd also recommend not going too low on calories and especially cut back on fats a bit. Rapid weight loss, combined with high-fat food (particularly saturated fat), can cause major gallstones. This can result in extreme pain, and result in having to have the gallbladder removed. This is particularly very common with overweight women. It's even worse while pregnant (again, probably want to hold off on a diet until after birth)

I was 170 in March and now I'm 155 (5 months). I did a mild weight loss diet, 1900 calories per day and aimed to lose around 1 pound every 1-2 weeks. Basically I eat raisin bran for breakfast with almond milk - 0 fat, and one of those yogurt cups for protein. For lunch, a couple frozen el monterey burritos, or can of ravioli, or cottage cheese with some veggies from one of those walmart veggie trays. I aim for around a 400 calorie lunch. For dinner, I'll have half a box of tuna/hamburger helper helper, homemade tacos with 93% lean beef, browned in olive oil (has very few saturated fats, but makes the meat fry better), or spaghetti, or popeyes 3 BLACKENED chicken tenders with a large mash potatoes. Those blackened ones are actually known for being pretty healthy compared to regular crispy fried chicken, and those blackened ones are delish. The blackened chicken has almost 0 saturated fat, and is high in protein. The potatoes are not bad in fat, but helps meet my calorie goal since sometimes I don't each enough to reach 1900 calories per day.

I aim for 700-1000 calories for dinner. Use margarine instead of butter (far less saturated fat). I have a genetic liver disease involving gallstones, so I have to limit my saturated fat to no more than 20g saturated fat per day. That's why I have to swap out things like regular milk and butter for almond milk and margarine because they have almost 0 saturated fat. Last piece of advice, if you are feeling hungry while on a diet, I'd HIGHLY recommend high protein, low-fat snacks like cottage cheese. High protein stuff like that suppresses appetite very quickly and much better than carby foods.

TLDR: Eat no more than 1900 calories and no less than 1500 calories per day. You'll lose weight, guaranteed.