Hi Jem,
Hopefully you have found the source of your problem by now and are feeling much better?
If not, then even though your tests came back negative for mono and Hepatitis, I think you still have some infection present. If you are having fever and upper belly pain on the right under your rib cage, which is where your liver is, then you have an infection somewhere. If blood work does not show up what is going on, then your doc may suggest a liver biopsy.
Good luck.
Sarah