Weight loss in second trimester

Anyone experiencing weight loss in second trimester? I'm 18 weeks today and have stayed at my preprgnancy weight up until now, and when I weighed myself this morning I'm down 3lbs! I certainly haven't been not eating bc I feel constantly hungry, but I'm still experiencing really bad morning sickness. My dr didn't seem to concerned at my last visit that I haven't gained any but now I'm starting to worry about baby growing properly and getting enough nutrients?