2. Ovulation.
Stringy discharge is typical for ovulation. It looks like egg-white cervical mucus, clear and usually white. Sometimes it can be with brownish admixture, but without odor or such symptoms as burning sensations and acute pains.
3. Sexually transmitted diseases.
If you are sexually active, and your brown discharge seems abnormal, i.e. too abundant, with unpleasant odor, accompanied by itching, burning or painful sensations, this can be a symptom of one of the STIs. Do a pap and blood tests, and they will show precise results. If it is possible, persuade your partner to do the same tests.