Unexplained hair loss

So I have really long hair. I know it’s normal for hair to fall out but mine literally falls out in clumps. The 2nd picture is what my hairbrush looks like after brushing it one good time. I brush my hair constantly throughout the day to get rid of tangles/rats. I don’t use harsh chemicals or heat on my hair. Is it normal for me to be losing MORE than this much hair a day?? It’s constantly falling on my clothes, stopping the drain, falling in the sink, and literally falling out.