Thick white creamy discharge, smells like onions and it itches badly?

Yeast: It says you are female, so the most likely thing is a yeast infection, although trichomonas and bacterial vaginosis is also possible. The best thing is to see a doctor to make the proper diagnosis. The next best thing is to try a topical over the counter medication like monistat.

Vaginal?: I assume you are talking about vaginal discharge. A common cause of white discharge is candidiasis or a "yeast infection". Alternatively, some bacterial infections of the vaginal tract can present similarly.