I Am 68 Years Old, Gaining Weight Has Never Been

I am 68 years old, Gaining weight has never been a problem until recently. I have gained 6-8 lb in a 6 week period. I am tired most of the day but by 9-10 pm my energy level picks up a little. I sleep 8 hrs a night. My shoulders ache and my lower back feels uncomfortable. My skin is extremely dry and itchy, I just feel bad all over with nothing in particular being wrong.