Discharge thats brown and its 3days before my period no pain or dicomfert what's going on?

Spotting. It is likey that the brown discharge is just a little blood mixed with discharge. As long as the discharge does not have a foul odor, you are not experiencing pelvic discomfort, you have not noticed any genital lesions and you have no fever i would suggest that you just monitor it. Wait to see how this cycle goes. If the problem persists, then see your doctor.
Premenstrual spottin. If you are on birth control pills , you may change pills to higher hormone dose pills or there is most of the time no problem make sure there is no cervicitis no vaginitis, no other vaginal lesion.