Hugs...I hope it's not cancer. One thought--did the fatigue start fairly recently? because that sounds a lot like the symptoms when I had mono in college. Including swelling of the lymph nodes on the back of my neck. Is your throat sore/swollen at all? The sore throat and intense fatigue were my biggest symptoms of it. It can be diagnosed by blood test.
That's good you're seeing your oncologist soon. Please be sure to go to the appointment, even if you're scared.