I am 15 weeks and 4 days pregnant. I am not going to ask how much you weigh but I will tell you I have actually lost weight while being pregnant. My Dr. told me it is possible if I eat right. your baby will get the nutrients it needs and then you will. I eat several small meals throughout the day consisting of fruits veggies or beans. I do not "eat for 2". I try to eat before I get hungry. That helps with not over eating. I also take about a walk 30 mins- 1 hour. I wouldn't try anything strenuous like running or weight lifting but I would recommend staying active. I also recommend drinking lots of water. I haven't lost a ton of weight but I have noticed my body changing. I hope you find this useful and good luck.
I wouldn't try to lose weight while pregnant but exercising during pregnancy is great for you. If you didn't exercise before you got pregnant than you'll want to start slow and not stress your body. Walking and yoga are two great low impact workouts for pregnancy. I just finished a yoga work out and I feel so good now.
I asked my doctor the same thing when I was about 24 weeks. He said exercising is fine. But nothing too strenuous & crazy. Whatever you did prior to being pregnant, you can continue doing. Your body is used to it. Walking is great while pregnant. Definitely talk with your doctor about it. I wouldn't start anything new other then the treadmill, yoga, or light hand weights. You don't want to put your body thru too much physical strain. But again I'm not a doctor. I'm just going by what mine told me. I know some excersises are definitely a plus while pregnant. It helps with a more breezy, healthy pregnancy & easier labor typically. Good luck!