You poor thing! I'd suggest that you call your doc's office to identify which tests they administered. There are a couple for mono. There is the Epstein-Barr Virus Antibodies Test and the Mononucleosis spot test. Doctors also order a complete blood count. There seem to be two possibilities right now.
1. You have a negative mono spot test with symptoms and reactive lymphocytes are present and you may be in the small number of people who do not make heterophile antibodies. Other EBV antibodies and/or a repeat mono test may be performed to help confirm or rule out the mononucleosis diagnosis.
2. You may present a negative mono test and display few or no reactive lymphocytes. This means that you may be infected by another microorganism that is causing mono-like symptoms (such as a cytomegalovirus (CMV) or toxoplasmosis).
When the mono test is negative and/or the doctor wants to obtain more information about the presence and status of an EBV infection, she may order one or more of a combination of EBV antibodies. These tests can indicate whether you are susceptible to EBV, have had a recent infection, have had EBV infection in the past, or have a reactivated EBV infection.
I hope this helps! I think you should return to the doctor and follow up. I'm rooting for you!