I have nexplanon, I got it inserted(into my arm, in case anyone doesn't know what birth control this is) in early August. Mid-august I had a period, a huge range of menstrual flow from spotting to heavy, for 7 days. My periods were normally 3-4 days and normal bleeding, not heavy, not light. Then I didn't have a period for 3 months. I got one in December and it was on and off, I'd spot then bleed regularly for about 6 days. I thought okay cool, my body has started to regulate itself. Same for January.  I downloaded this app, put in my past period for January and expected one to come in February around the 15th. Didn't come. I for sure thought it was going to come because I had been pms ing for days, my boobs hurt, mood swings, cramps, back pain, the whole nine. My pms continued for another week and a half, then I got my period. But I only bled really for 2 days, the other 2 days were spotting. Very lightly. 
Does this all seem normal? 
It's driving me crazy to not know when to expect it, if it's going to be on time, light or heavy, etc. 
anyone else who has this birth control let me know what your experience has been this far, please. :)