What could be the cause of a low grade fever for almost 2 months? (99.4-99.8) my normal temp is around 97.8.

Temp elevation: We really would not consider this a fever, but it is certainly a change from your baseline. There are a number of possibilities - from a low grade infection, such as sinuses, pelvic, intraoral -to non-infection causes such as low grade inflammation somewhere or metabolic, such as mild hyperthyroid. You need a head to toe exam from both doctor and dentist. Write down anything else unusual recently.