I'm just wondering, if you have already had whooping cough, do you still have to get vaccinated?

A good idea. Even prior episodes of whooping cough (wc) do not give you lifelong immunity.Bacterial infections like wc can give a temporary immune boost, but this will wain over time like the vaccine. After several years, your system can be re-infected & spread it to others. While adult episodes are seldom life threatening, they may transfer it to infants that can die of the disease.