Plan b side effects

I took plan b 8 days ago and I’m in a lot of pain. I have terrible lower back pain that is restricting what I can do in a day. I also have cramps that are beginning to ease up but are still very painful, much more than my periods usually are. 4 days after taking the plan b I started bleeding (dark red with lots of clots but not as much blood as a regular period). Did any of you experience the same side effects? Is this normal?