I've had a lot of brown discharge for about 3 weeks now after I got my period... Which was late and abnormally light and long... What could be wrong?

Brown = blood . You will need to see your obgyn for an exam and testing. Depending on your age and fertility plans there are lots of treatment options. Birth control pills can regulate your cycle. Mirena (levonorgestrel) iuds can minimize your periods. Lysteda is a great new hormone free drug used to stop heavy periods. If you are done with pregnancies ask if you are a candidate for an endometrial ablation.