There are many reasons that women might gain weight. Sometimes it can be helped through better diet control and exercise, other times it might be due to medical conditions and medications, etc. Regardless of the reasons, it can be very stressful for women who don't fit the "average" mold to go shopping and find stylish clothes that fit them well.
Fortunately, there are stores that sell plus size dresses, pants, shirts, sweaters, and undergarments that are both stylish and designed to fit a woman. Let's face it, women have curves, and many of us have a few extra pounds we carry around. The larger department stores in the mall are beginning to carry more stylish Women's size clothing, but it can still be hit or miss. Online and specialty retailers are much more focused creating stylist, not frumpy, plus size clothing.
If you find it difficult to find stylish clothing to fit your size, I encourage you to look around online to see what's available. I think you'll be happily surprised to find most of it looks better than what you see in stores!