My girlfriend is not on her period but has had a lot brownish type blood coming out for the past 2 months. what could be the cause of this? thanks

Vaginal bleeding: There are too many possible causes of abnormal vaginal bleeding to even guess at the cause. She needs to see her doctor.

Dysfunctional bleed: Is she on BCP? Normal periods or lighter periods? . There is some variaiton in periods but 2 months is a long time ma ybe realted to BCP if on them otherwise check for miscarraige, polyps, fibroids, horomonal abnormality-sometimes occur w stress as well. Check blood HCG and follow up w/ doc may need sonogram