Pregnancy

So I'm already 2 weeks late for my period. I got my new nexplanon in my arm like a month ago. A week ago I was feeling weird. Having bad cramps and nausea, thinking it was gonna be my period. Well I went to the bathroom, had some pink discharge thinking it was my period and then it stopped. I took a pregnancy test and it was positive. Took another one the next day and it was negative. Went to the doctors and it was negative. I still haven't gotten my period. If it's not pregnancy what do you think it could be? Chemical pregnancy maybe?