Cramps for 8 days.

Jessica • 24, England, implant out in Jan 2014
I have been having period symptoms for 8 days but no bleeding. I came off implanon in January and have had cycles of 29 and  21  three periods in all this cycle im on 29 days. Feeling so so down starting to panic  that something is wrong with me. How can I be havering cramps for 8 days with no AF