Vaginal swab

Hi anyone tried doing vaginal swab before during your prenatal checkup? How’s the process? Is it just a normal swab and we can get the result instantly or the doctor need to get a sample and send to lab and we need to wait before she prescribed with medicines? How much is it? Am in my 2nd trimester. Having increased yellowish vaginal diacharge. Suspect maybe it’s yeast infection or something.