What causes dizziness all the time?

Constant dizziness. Dizziness describes different sensations to different people. Do you mean a spinning sensation, a feeling of faintness, or a sensation of unsteadiness when you walk? These different symptoms can be caused by disruption of different parts of the balance system. Inner ear inflammation, a tumor along the hearing/balance nerve, heart muscle or rhythm issues, brain anomalies, medications, among others.
Several causes. A compete history and physical can usually come up with an explanation. The word dizziness means different things to different people, so a detailed description of your symptoms is needed, as well as your medical history, medications, age.