Ovulation or Implantation?

I have always had irregular menstrual cycles. They’ve never been monthly, they’ve always been more bi-monthly. Meaning the average time between each of my cycles is about 60+ days. My periods last about 6 days and are always heavy from start to finish. I usually get a bit of warning spotting 24 hours before and I usually get normal light brown discharge 24 hours after my cycle ends. My last cycle ended on November 8th. I had sex with my fiancé on both the 9th and 18th of this month unprotected. The past 2 days I’ve noticed light pink and pale brown discharge, I had some abdominal discomfort that really resembled period cramps on either side of my pelvic region, and I was a bit nauseous with a headache for a better part of the day. I read up on ovulation bleeding but since my cycles are so long I never know when I’m truly ovulating. Also, I’ve never had that symptom near ovulation before. Is this implantation bleeding?? Please help!