What is my moms' obsession with my weight?

I'm one of those individuals who has struggled with weight my entire life and have always had a mother there to remind me that she's not pleased. Despite dieting and exercising, I tend to carry a little extra weight. And I really mean a little. I'm 30 years old, married, and have a very credible profession, yet my mother feels the need to remind me every time she can that I need to lose weight. She'll make passive-aggressive comments about me eating too much when we go out to dinner and I order a grilled chicken breast and steamed vegetables. She also texts me to watch television shows on weight loss and will insist that an outfit she bought me is too small, even when I will try it on for her and it's hanging off me. My husband will also be commenting that the garment is too large. The fact is I do weight watchers and run almost daily. I've done this for years, since high school. For some reason, after a cross country move, I was able to drastically lose weight, almost too much. My mom loved it! I don't know why I was able to lose weight at that time. It stayed off about a year and gradually returned. I'm eating and exercising the same way if not more drastically as I was then. I've been to see doctors with no explanation offered. I just don't understand why she is constantly on me about this and it REALLY affects our relationship to the point where I want to move away from her. I don't know how to address this with her or how to handle it. I'm ok with where I am and my husband thinks I'm beautiful. She seems to be the only person with the issue. Any suggestions would be greatly appreciated. Thanks :)