A lot of times one-sided headaches can be migraines. I have had migraines since the 4th grade (I am now 50) and they are ALWAYS on the right side. I rarely get a headache in any other part of my head. It always starts with what I call "the lightning bolt" feeling behind my right eye then pressure behind and to the side of my eye like it's being pushed out of the socket then the pain starts. Sometimes I get nausea but not always. It always lasts exactly 24 hours and after it's over I have a horrendous craving for carbohydrates. Very weird. Midrin helps but I find sometimes Alka Seltzer works better because it's just plain aspirin and it gets right into the blood stream.