Thanks for the query.
Yellow colour foul smelling vaginal discharge
indicates infection of vagina with trichomonas vaginalis
Its called trichomoniasis
Diagnosis is by vaginal examination and swab test.
Metronidazole is treatment of choice but should be avoided in first trimester of pregnancy.
will not adversely affect your fertility. But it may cause miscarriage and preterm delivery.
So get your infection treated before you try to conceive.