What Causes Pain In The Lower Abdomen Followed By Spotting?

i have clipped my tubes many years ago but i have been having very painful and extremely heavy periods. Two weeks ago i decided to get primolut so i could delay my period as i was travelling. I finished my pills and the day after the last dose i went and got the depo provera shot. I disnt get any bleeding until five days later when i got very painful lower abdomen pains and spotting started. What should i do?