After getting married how soon can I get a work authorization that would allow me to switch my current job to any other company?

Generally in a marriage-based immigration application process the foreign national would also apply for an Employment Authorization Document (an "EAD" or "work permit"). The USCIS generally can be expected to issue an EAD within approximately 90 days of filing, and the EAD will authorize any lawful employment (without need for a sponsoring employer) while the Adjustment of Status application remains pending. It would be wise for you and your fiance/fiance to consult with an immigration attorney who, after learning all of the relevant information about you and the person you plan to marry, could advise you about immigration eligibilities, options and strategies and who then could offer legal representation in the often quite complex application process.