What Causes Hot Flashes And Elevation In Temperature Of Body?

I am 65 years old. Started menopause when I was 38 and took hormones til 60 yrs.Four years ago I underwent a 5 hour surgery to remove a portion of my tongue, lymph nodes & salivary glands. Why do I experience hot flashes 24/7? My body temp is normal at 97.6 and sometimes jumps to 98.8. Family doctor recommends I consult my oncologist. Any ideas?