Is it any way possible.....

That even though I am on the Nexplanon birth control arm implant, and have been using condoms lately, (there were a few times without a condom) but the last few times we have used them... My period seemed late (which I've never had regular periods) and now I'm crampy, and have a really dark brown period, just a tinge of blood, not very much.. Not discharge though for 2 days... Could I be pregnant or just symptom of BC?

I've had this BC for over a year, and ever since I've never had long or regular periods.. What could it be?!?!?!?!??