Normal...?

So my period is usually very regular. But just recently it’s been acting weird . My last period was Jun 1-15 it was 2 weeks long which isn’t normal for me it was so heavy I had to change like every 2-3hours. Then I missed a period for 71 days. I tested everything was negative. I even went to drs to get blood work done and again negative. Then just right now I got the worst cramps of my life. I went to the bathroom

And I’ve seen like brownish-red blood on my underwear . Not enough to like say it’s a period. But doesn’t look like spotting either. It’s just a smear of brown stuff. Is it blood or discharge. I’m on Nexplanon. Been on it since May 18. I’m just trying to figure out what the hell going on