Some women with secondary amenorrhea experience weight changes without any reason at all. Your weight may either shoot up or go down rapidly. The best way to shed those excess pounds off is to exercise more and adopt a much healthier lifestyle. On the other hand, if you’re underweight, try to eat more nutritious and healthier foods. 

Unless physical, there’s no need to take special medications for any of these symptoms. What you can do is to have the initiative to obtain the right weight for your body. Regular exercise and a proper diet can usually resolve the problem.