infection down there

any mummies is referred to dsc clinic? kkh called to say i have infection and have to take my antibiotics by tonight @UO&G and dr referred me and my partner to dsc clinic. first swab at 24 weeks preg, was cleared with no infection recent swab, 35weeks preg, suddenly have infection. kinda confused now. me and partner hasnt been having sex since known pregnancy so im confused and worried what may be the cause :/