Do I need glasses or is this normal?

I'm a 17 year old male and sometimes I have these strange eye troubles. First off, when im not focusing on anything, everything up close I see double. Second, im able to make my eyesight go in and out of focus at will (kinda feels like flexing a muscle), but after awhile my eyes hurt from doing it. Third I have trouble focusing while reading with both eyes open, so I normally read with just my right or rarely my left eye. Lastly, I seem to have better vision in my left eye then my right. Does this mean I need glasses, or is this normal?