Pls can u advice if mild fever can be due to symptoms prior periods? thanks

No: Periods are usually not accompanied by fever. Perhaps your period coincided with an infection such as a cold or something else, but normally periods are not expected to present with fever, even mild.

Mild fever?: You need to define what you think is fever. Many think it is a temperature over 98.6 f and it is not. You generally will not have fever due to your menstrual period. Something else may be going on.