What Are The Side Effects Of Contraceptive Injection?

Hi, I had the contraceptive injection on the 6th dec 2010, I was ok for a week apart from headaches, but then I started bleeding quite heavy...I decided not to go back for the next injection as my doctor said my iron levels had dropped a lot due to the bleeding. I was meant to have the next injection in the first week of march, when will it be out of my system as I am still bleeding heavy now, i have been given transemnic acid to help cope with this.