Why Do I Have Severe Pain After Stopping Duphaston, And What Painkiller Can I Use?

I have a cyst. I took duphaston last mont for ten days, when I stopped taking the pills, 2 days after my bleeding is start, and now i have a very bad pain that l can not do any thing, I experienced these pain before when i used duphaston, i want to know why is pain occurred? And which pain killer can i use for reducing the pain? I appreciate for your help.