How much do your PMS symptoms vary?

I thought i had the most screwed up cycle. Sometimes i bleed for 2-3 weeks. I stop then start spotting again and then at times it's so heavy that i'm afraid to leave the house.( i have bled through my clothes in a matter of a few minutes of changing.) I'm been to the doctor and they tell me nothings wrong and it's normal. So i just live with it. It sucks.