Why do you get a headache when you read in the car?!

Because you are tightening up your neck muscles to hold your head as well as hold what you are looking at still. It's a double whammy for the muscles. You can free up your neck muscles to get rid of the headache and that should keep it away as well and here's how to free them up:
Neck
Put your hands alongside your head so your thumbs are on the front of the muscle under your ear and your fingers are on the back of the muscle behind your neck. Squeeze your thumb and fingers together and hold. Relax your body. When your fingers and thumb touch, about two minutes, slowly lower your head as far as you can, release the pressure but hold your neck lowered for another 30 seconds.
For best results relax the body first by taking a deep breath and exhaling then remain this relaxed.

it could possibly be motion sickness

experience

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