I just developed fever 100.5.I was fine before that. No other symptoms. What is it!? By the way I never have fever even when I'm sick.

Wait & see. I don't tell patients they have a fever unless their temp is over 101. Small elevations in body temperature can have any number of causes, from minor viral infections to over-exertion or over-exposure to heat. Keep an eye on your temp and try to stay cool; if your temperature continues to rise, then you need to see your dr.