I have noticed that my mother is having a mild fever since many days. And this is not the first time around some before she used to have same condition in her body temperature remains 97-98.5. And again this is happening since a week and some time her body temperature is normal and sometimes it's 98-98.5. I'm confused why this is happening. Last time we noticed that when ever she do a work like preparing food and other household work her body temperature increases