What Causes A Mild Headache?

every evening after around 4:00, i start having a little headache, nothing terrible just bothersome and annoying. along with this, my body temp rises just enough to make me uncomfortable (around 37.1 deg C). i have also been having trouble with my thought process (like confusing days and times). i am not sure if all these things are related, but they bother me. any ideas?