The brownish discharge usually denotes the stale bleeding. May be while finguring, you could have hurt some tissues inside the vagina or may be your hymen (a membrane at the vaginal opening) was mildly scratched or hurt but not completely torn. This can cause slight bleeding. Vagina is very expandible organ and can store lot of fluid into it. So could be that this small amount of blood has been pooled inside your vagina, and now it is coming out with your cum or when you are upright . When aroused sexually, the women always have lot of vaginal discharge and that makes them wet. When that comes out of vagina, it is called as cum . I feel gradually your browny discharge will become clear. I have to advice you a couple of things: 1. While mansturbating or may be having sex, please do not use dry articles, not even your fingers. even though you are fingering your clitoris, use wet fingers. Simple clean water is OK. Or you may go for vaginal gels available. 2. When you are using naked fingers, first clean wash you hands before fingering. 3. Please cut your nails short before you finger yourself. 4. If you use anything like gloves, fingerstalls or condom, please take care not to even touch the pee hole lest it causes inflammation and then the infection of urinary tract. It may then rise right upto the kidneys to infect them. This is known as honeymoon pylitis. Better do it under vision.