I would recommend that you see a doctor
. Requiring 12 hours a day of sleep is not normal, and could be a sign of many diseases (one of which is depression
). I would recommend that you start by seeing your primary doctor.
As you mention, depression can cause fatigue and an increased need for sleep. That being said, in order to make the diagnosis of depression, the feeling of sadness or the inability to feel happiness is also required. Other signs of depression include feelings of guilt, lack of concentration, suicidal thoughts, lack of interest in previously enjoyable activities, decreased movement and decreased appetite. If these (or at least some of these) don't apply to you, depression is unlikely the cause of your fatigue.
There are many other causes of fatigue. One that I would worry about is low thyroid level or hypothyroidism. This causes fatigue, feeling of cold, and constipation. This can be checked by a simple blood test. Another common cause of fatigue in women your age is a low blood level or anemia
. This can commonly caused by excessive menstrual bleeding. This again can be checked with a simple blood test. There are many other causes. Some of these are easily fixable -- so please see your doctor.