What Causes Sudden Weight Gain In An Elderly Person?

Thank you for taking my question. I am 57 years old, had my last period 8 months ago, have gained about 15 lbs in that same amount of time, I sleep sounding for 10 hours a night and could easily sleep 16 hours a day if I didn t set an alarm. I am sleepy most of the day and do fall asleep if in the afternoon if I sit down to read. I am usually a hard worker and work until I hit a wall, when I come to a full and complete stop. I then sleep up to 48 hours without any problem. I am concerned because I feel like this is not normal behavior. I also am struggling with the fact that I have gained weight. Any thoughts?