how early after conception can you test for pregnancy?

Lozzie
MY implanon is still in, final date on the card was 30th September 
I had numerous unprotected sex all that week and on that day as well. 
My period was due 1st October, no signs of it yet. 
Is it possible to be pregnant? I thought the implanon took about 14 days after its final date to properly expire, and how early can I use a pregnancy test after conception? 
It's bugging me cos I was going to put another implanon in for about 6 months then we were going to try.... and I need to either go ahead or cancel the doctors appointment which is this Monday 10th October. 
What would u recommend??