Could be a variety of things. It's usually a yeast infection. The bacteria yeast are always living inside our bodies. Sometimes if your immune system becomes weak or if you have an imbalanced PH it can trigger the yeast population to explode. That's why it is common to get a yeast infection after a woman is taking antibiotics.
You should have it checked out by a doctor regardless. It could be vaginitis
. This is a general term for any bacterial infection.
Regardless you should have it checked out by your doctor.
Oh and don't use antibacterial soaps. It can only make your situation unbearable take it from me!