Period or pregnancy?! Mega confused

So Igor my Mirena out in June. Since then I have had very regular but slightly lighter than what I remember them being before Mirena (I had no periods while on Mirena) this month I spotted the last three days and now it seems to be almost done- I've never in my life had a period that light. I am so confused...any suggestions?? I am just lost it's been just spotting and I sooo don't understand what could be going on. I know that a really light period could be a bad sign about my uterine lining- should I be concerned?