You should still get the second dose to be fully protected against getting COVID-19 again, but you should not get a vaccination while sick or during your isolation period to avoid spreading the virus to others. You can get the second dose as soon as your isolation is over, and it has been three or four weeks since your first dose [a minimum of 21 days for Comirnaty (Pfizer)] or 28 days for Moderna, and a maximum of six weeks or 42 days for both vaccines). If more than 42 days have passed since your first dose, you should still get your second dose as soon as possible. The Centers for Disease Control and Prevention do not recommend getting a third dose if you fall outside of this time frame. For more detailed information, visit https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html.
For more information on the difference between isolation and quarantine, please visit https://www.cdc.gov/quarantine/index.html.