I've been sick with something since the 26th. How long does the flu last?

The main issue for me, is that I need sleep. Lots of it. Yesterday, I slept all day. My ears ache a bit, wake up in a sweat (fever broke?), not a ton of energy, headaches, and at times, my stomach feels off.

I have a doctor’s appt. for next Monday. If it’s a flu that will run it’s course, I’ll cancel the appointment.

Another question, how do we know that it’s gone from a flu bug to something else. Say, a viral infection, respiratory infection, or sinus infection, etc?