I need advice on what's this gooey white stuff in my vagina and underwear?

Could be infection: If you are having a different discharge than you usually do. Then you should probably seek medical attention. The appropriate venue is through a primary care provider or a gynecologist. You could have a yeast infection. This is caused by an imbalance in the acidity of your vagina. Especially if it is causing itchiness and foul odor. Your May need anti-fungals or antibiotics.