Is this spotting implantation?

I am not sure what my cycle is since I just got off the dep shot 2 months ago. I was only on it for one cycle though. Anyways, on Sept 17th I had my first period since being off the shot. we have been trying to get pregnant since september. Today I had some spotting. Is this just a period coming or is it likely this is implantation spotting? After implantation occurs, how soon can you test?