I am a 4 mile a day walker sometimes runner. Why would my thigh hurt from my hip joint down when I move my leg side to side? Walking doesn't hurt as bad as sitting or lying on my side or trying to lift my leg to roll over or slide into the car seat?

While . While it would be impossible to make a diagnosis completely on your symptoms, it's quite possible that the pain is coming from the hip joint. This could be arthritis or even a tear of the gasket around the hip joint called the labrum. An orthopedist should be able to give you a diagnosis with a basic physical exam and xrays. The hip tends to be most painful it sitting positions and lying on the affected side. I'd suggest seeing an orthopedist who specializes in hip disorders/joint replacement.
Hip bursitis. Runners are a set up for a hip bursitis -- which is an inflammation of your iliotibial band over your greater trochanter. The other issue can also be a labral tear of the hip (i.e. A tear of your cartilage).