Everything in your post points to a bad battery and a possible bad alternator. YOu say you bought the car in 2008 but do not mention ever replacing the battery - while measuring voltage is a good idea, if that battery has been in there since 08 or earlier, it is time to replace it. Just how long do you think a lead-acid battery lasts?

One more thing:
Continuing to drive a car with such indications is dangerous, unstable voltage caused by a battery's open cell can damage the (very expensive) modules in the car.
Leave the car home until you resolve this.