Candidaisis is not Sexually transmitted diseases (STI)

Vaginal yeast infection (also called candidiasis or vaginal thrush) is called by yeast fungi of the genus candida. 75% of women have vaginal infections once in a year. Candida fungi are normally present in the body and causes no harm until there are changes of Vaginal PH thats when thick white discharge starts and itching too.

Candidiasis is not STI. It is caused by loe immune function, antibiotic intake or pregnancy, diabetes and douching etc. 

Consult a doctor.