What Causes Painful Periods?

hi sir/madam, i am a woman aged 33 and i am married for the last 16 years. i have a son aged 11. since the beginning, i used to have very painful periods. i was told by doctors and others that the pain would go after marriage. however not much has changed. i still have very painful periods and the period lasts for 5-6 days. last month (27 may 2011) i got an iucd inserted by my gynecologist. however, since insertion i am feeling abdominal pain specially in the left side lower abdomen. i consulted my doctor who advised me to go for a tvs. the tvs showed 1. bulky uterus 2. functional cyst in right ovary 3. fluid in POD. my doctor has not prescribed me to take either 10 placentrex or sterodin injection on alternate days. however, i have been told by the medicine store people that placentrex is a banned drug. i also surfed on the net to find that the drug has some safety issues. i don't know why my doctor has advised me to take such a banned drug. in the light of the above kindly let me know 1. what exactly is my problem 2. which of the injections shall i take, or whether i shall take any of the injections or not at all. plz reply elaborately.