Hey, i wouldnt worry, implanon can cause strange changes in womens period patterns...i have it and dont get any and ive heard of women who also didnt get any for the first two years and in the 3rd year they had really bad ones....so it can change them.
As for being pregnant, i very much doubt you are...especially not in the 1st or 2nd year. my nurse told me that there had been no recorded pregnancies when women were on it and if they were preggo, they had conceived before they got the implant....its supposed to be almost as effective as sterilisation and more effective than the pill ( i found a graph thingy telling the effectiveness of each B/C and the implant was at the top)
Mind you, not all b/c is 100% effective, of course, but its unlikely theres a chance of pregnancy, even if you wernt on the implant; you were on the last day of your period...an unfertile day so id say your all good.
If your worried tho, its best to see your doctor.
im so sorry about the typing errors