I can't really answer the qustion for you but... I was in the same situation as you, your not meant to have a period on the injection, but your not meant to have big clots either, have you been to the doctors? If it was me I wouldn't worry too much it happened to me when I was 16 and I took 2 years for my body to get back to normal and I'm now 19 and I have a beautiful little girl... my advice to you is to go see your gp and tell them that you really think something is wrong and see what they can do for you... GOOD LUCK!!