I'm 51 year old woman never been over weight till this last year ?

Perimenopausal?: The most likely cause is the combination of changes that occur as we grow older, "the change in life". Visit your Doctor to check all your Hormones, and especially your insulin levels, as high levels sometimes influenced by the decrease in hormones and our present diet makes it hard to lose weight. The good news, we have diagnostic and treatment options to counteract it and age gracefully.

Weight gain: would advise a physical exam and especially a thyroid function test and a fasting blood sugar with a full metabolic workup.Diet, exercise, a hint: put up a photo of yourself looking great at your best weight and paste it to your dressing mirror. Your brain will do alot of work for you. Diet=4 F's-fish, foul. fruit and fiber. High and low burst interval aerobic exercise: look at photo daily.