Pregnancy with mirena?

So I have had my mirena in since September 2016. I hadn't had sex for several months prior to that, and didn't have sex until 2 weeks ago. The mirena completely took away my periods and my cramps immediately. I had sex without a condom from Jan 3-8. Didn't think I needed it with the IUD. All of a sudden today I started having horrible cramps on the left side of my pelvic area and I spotted once while I was going to the bathroom. This hasn't happened to me since September. I am worried about the spotting being implantation bleeding. I know it's super rare to get pregnant with the mirena, but it is possible. And I'm concerned because I have read that pregnancy with the mirena has a higher chance of being ectopic.. is it too early to take a test? If I am pregnant I need to know immediately so I can rule out ectopic. I can't exactly wait for a missed period since I don't get it anymore. I don't know what to do.