If you ARENT' ALREADY AT THE DOCTOR, go NOW!
I agree with the others on the not-seeking-medical-advice-on-the-internet thing.
I did have those very same symptoms and I thought I had a back ache along with the flu, but after I went to the clinic and was diagnosed with a kidney infection, I was admitted to the hospital. Once they got the Levaquin in my system I started to feel better almost immediately.
The moral of the story is: Go to the doctor when you are sick.