I took the depo twelve weeks ago and now ive been cramping for the past week and it wont stop

Patient: I took the depo shot for the first time july 5, 2011 and i did not have a period for two months. but just recently i started my period of september 5 and it was normal i bleed for five days then it stopped. around the 16th or 17th of september i started cramping and then i was spotting a little around the 20th. it is now the 26th and i have not spotted agian but i am still cramping. could this mean i am pregnant agian or is it just a side effect of the depo.. i think it is to soon to take a pregnancy test