The answer to your question is YES! Symptoms can vary day to day as well as the severity of the symptoms. I think your doctor is way off base and you need to find a new one.

A really good book that you might want to take look at is "Brainlash" by Gail Denton. It does a great job explaining what is going on. I think ever doctor should read it. Then maybe we wouldn't get "it's all in your head" or the "suck lecture".

"Over My Head: A Doctor's Own Story of Head Injury from the Inside Looking Out" by Claudia L. Osborn is also very good.

Hang in there find a doctor a new doctor.

(BTW - My daughter is 15 and suffered a concussion back in October. While not 100%, she is significantly better during the first couple of months.)