Implantation?

I have been having very dull cramps for the last 3-4 hours and about 2 hours ago started lightly spotting. It was brown at first and now kind of a pinkish color. It hasn't been very much at all. I had my Mirena out about a month and a half ago and haven't had AF yet so I don't know when I ovulated or when I should expect my period. This doesn't feel like a normal period though as I never started with spotting. I always just had a huge gush at the beginning of AF with a heavy flow for 3-5 days. Been ttc for about 3 weeks now. BDing every other day. What are you experiences with implantation and do you guys think this could be it?