What Causes White And Sour Smelling Discharge After Sex?

I let my boyfriend come in me for the first time, and he is the only sexual partner I have ever had. I am currently on birth control so I'm not really that worried about pregnancy, but ever since then, my discharge has changed. It is a creamy milky white and has a sour odor. Not fishy but almost like vinegar. This odor gets more prominent after intercourse