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.