Weight loss

I am 12 weeks pregnant and since finding out I was pregnant at 4 weeks, I've lost 10 lbs. Not really doing anything different. I am 5'0" and my original weight was 155. Obviously I'm overweight but not too extreme. Has anyone else experienced this? It's been mostly in the last 5 weeks, since my last dr appt and I go back Thursday. Just wondering if I should be concerned?