What can cause brown/black blood every period, sometimes swollen and blood during sex?

Normal: It's normal to have brown/black blood every period. Darker blood is just older blood. The uterus not evacuating quickly when there's blood there. You didn't say what was swollen, so hard to answer that part of question. And blood during sex would be normal during period. If not on period, could be from cervix or uterus. If cervix, make sure pap utd. If uterus, can be polyp or fibroid.