Hi thanks for your question.
Pink discharge could be due to infection of the vagina or cervix
and every infection of genital organs doesn't mean STD
that is inflammation of cervix and vaginitis
that is infection of vagina can give rise to pink discharge. There are millions of organisms in the vagina both good and bad, a balance is kept between good and bad organism due to many factors present in vagina. Any bacteria can cause infection of vagina leading to pink discharge. There are many factors which cause inflammation of cervix, which could also give rise to pink discharge. Consult a gynaecologist who may examine you to determine cause of discharge. He/she may take swab for culture from your vagina.
Hope this answers your question