I Am 51 Years Old The Week Before Christmas I

I am 51 years old the week before Christmas I came down with a stomach flu, the week of Christmas a terrible cold though most of the cold systems are gone I am still feeling completely exhausted no energy at all almost like I haven't sleep in a month and continued nausea. This is not like me at all I am hardly every sick and it just seems never ending and I usually have lots of energy. I am wondering what this could be symptoms of and if I should see a doctor.