Slight Concerns

I got skyla back in January. I've had two periods since. Each were about 14-16 days apart with some spotting here and there. My third one was supposed to start 8 days ago. I took a pregnancy test two days after it was supposed to start and it was negative. (I know chances are low but I'd rather be sure) My boyfriend has never finished in me, we typically use pullout. I've had some cramping like I'm on my period but still no sign of blood. Any suggestions? Experience?