Could be a bacterial vaginosis infection, similar to a yeast infection, but I believe more common. You should contact your doctor, only prescription based meds can cure. And can cause other problems if not dealt with.
Most of the time, this is a clear indication of a yeast infection. If you have treated yourself for a yeast infection and you still have this occurring, seek medical help immediatley. This could indicate a possible STD.
A sour discharge signifies that the environment in the vagina is acidic, which in itself is not necessarily an issue. The cause of the acid environment does however need to be discovered and treated. It is most likely a yeast infection by Candida, but needs to be seen by your OB-Gyn.
