Weight loss during pregnancy?

Hello new and experienced moms. 
I have a question for all of you. I am currently on my third child and about 17 weeks. With my other two pregnancys I lost some weight during. My last one I lost 20lbs and my daughter came out 8lbs. I have currently lost 14 lbs this pregnancy at only 17 weeks and my Dr is concerned. Has anyone else experienced any weight loss like this?