What Are The Side Effects Of Using Depo Provera?

hi i was on depo provera and i was suppose to get my next shot in december but i didnt want it no more so i missed it..i started my period at the end of april to the beginning of may and it last for 14 days..my cycle used to be a 21 day cycle but i dont kno if its messed up now...i have been sexually active (protected). could i be pregnant, i dont know why i havent seen my period at the end of may..can you help me?