Supplementary Oxygen is usually used at very high altitude, like above 8,000 meters (26,247 feet) in the Himalayas. It will do nothing for you on Mt. Whitney except waste your money.
The fastest cure for altitude sickness is to quickly go to a much lower altitude. Even 1,000 lower will make you feel better, but you must continue going down in order to prevent additional complications.
There is a lot of information here about altitude sickness prevention: read it.
