body seems to be just losing weight without trying to

I'm a 19 year old female, 5'1 and my usual weight is around 96lbs but lately my body has just been losing weight and i don't know why. I currently weight 89lbs. I eat normal and nothing has changed in my diet or how I live day to day I cannot figure out why my body keeps losing all this weight. Does anyone have any suggestions as to how to keep my weight at a constant?