BBT novice. What am I seeing?

Carilyn
So we're TTC and I got my Mirena out on what I think is CD20. I'd been spotting a bunch because the IUD was embedded w/ a lost string and I had to have multiple apt's/attempts to get it out. All attempts were within this cycle and caused bleeding. Eventually it was removed with a hook and ultrasound, then I had what I think was intense withdrawal bleeding. Yesterday (4/27) I started what I think is my first "real" period. So CD1 on this chart is an estimate based on my lowest temperature that month. Is that a somewhat accurate way to guess? And did I ovulate this cycle? Does anyone know if the intense variation at the beginning is because of Mirena?  I'm super confused since my bleeding and temps don't match. Should I/when should I start using OPKs on my new cycle? Thank you in advance for any advice to get me back on track!