What Causes Missed Period While Having Expired Implant?

My implant was expired in January 2015 the doctor told me I was fine I could come back in two weeks and get it removed I have read the symptoms but I haven t really experience them until now my period has always came but now I m having pregnant symptoms I haven t come on this month which is the first time and im spotting on and off when I had sex dark blood got on him but nothing was on me...confused right now need answers