Hi, I was implanted with implanon nxt in sep 2011. I haven't had a period until this morning. It is very light. Should I be concerned?

No. You have done well not to have had any bleeding until now. Occasional (and unpredictable) light bleeding is normal.
Not necessarily. With implanon, some women continue to have periods, irregular periods or no periods at all. So, your light period could just be normal with the implant. Hopefully you are still getting checked by the dr. That placed the implant. I would recommend being examined at least once a year while on the implant. This also varies from provider to provider.