Weight gain

So before I got pregnant I weighed 170 because I never lost my baby weight from having my son, and when I went for my 9 week ultrasound I had gained 3lbs, I just went back at 13 weeks and have lost 7lbs. I've not changed anything so idk why I've just all of a sudden started losing weight. Although I have had terrible headaches that last for days and I throw up everyday I have one. Could that be why?