Concerned about implant and pregnancy

I have been on the nexon implant for nearly three years in January 2014. Recently I have been on avicclor antibiotics for shingles, four sessions of antibiotics within five months. I'm now really worried that this has made the implant less effective. I had unprotected sex while on the antibiotics and now I'm experiencing pregnancy signs. About four weeks ago I had slight bleeding, just a few drops of blood. A week after some creamy thick discharge, now I've slight cramps, back ache, dull ache in boobs now & again, tiredness even after 11hours sleep!!! Feeling sick & hungry at the same time, mood swings.Has anyone got pregnant on the implant? Are these pregnancy signs? Please reply :)