Hello
You are taking sulfamethoxazole+trimethoprim , that's right but this never causes any
vaginal discharge , however, in few cases this causes hypersensitivity reaction so this may be the cause of
vaginal irritation .
But this allergy ( irritation occurs on day 1-2 as you start this drug ).
These are symptoms of genital herpes simplex :
Can be asymptomatic , subclinical , mild or severe.
Incubation period 2 to 12 days .
painful vesicular lesions/painful ulcers and
tender lymphadenopathy occurs.
Lesions are usually multiple.
Can cause urethritis and cervicitis , which can not be distinguished clinically from chlamydia and gonorrhea .
Diagnosis can be confirmed by culture ( gold standard ) , highest yield with vesicular lesion ( as from vaginal swelling )
PCR
Type specific serology
cytological changes.
So in my opinion don't think so and at once
consult a dermatologist and get his opinion.
Hope this will help you.
Milky yellowish discharge is due to infection ( cervicitis amy be the reason )