It is quite likely you have a virus. There is a lot going around, and viruses often cause fevers in the range you describe. Being sick might change your period, also. Try to walk around a bit instead of sitting still.
It is a low grade fever. It isn't anything to worry about. It sounds like you are still fighting a virus. The temperature will go up when you are fighting something. If it goes up to over 100 I would see your doctor. Your period may be late due to having an infection.