Is a temp of 99.5 for over 2 month's considered a low grade fever. Or cause for concern? I've had multiple test but nothing diagnosed yet

Depends. 99.5 isn't necessarily a fever. Some people have a higher baseline temp than others so that may be normal. The diagnosis also depends on whether you have any other symptoms.
Unknown. Maybe that is your baseline body temperature if you feel fine and the testing has been normal thus far.