What Causes Painful, Irregular Periods, Spotting, Fatigue, And Dizziness?

I have spotting before and after my period. I have heavy, really painful periods with large blood clots. The pain gets so bad that I can t walk or even get out of bed sometimes. The pain is before, during and after my period and the pain is in my lower abdomen and lower back. I always feel bloated and fatigue. I feel dizzy/light-headed when I stand up or change positions. My period is irregular. I also get bad headaches. This has been bothering me for years now.