New to tracking periods.. Help?!

Well not totally new... I tracked before ingot pregnant with my daughter, but that was a "wasn't paying attention, we should be fine" type thing with my ex. Lol. I have Mirena, I am in the process of getting it removed, hopefully next month. I've not had a period in two years. I know I ovulate, but I don't bleed. It's kinda nice. I'm tracking my CM the best I can, but when Glow asked for my last period and how long my cycles are on average I just kinda guessed at it. So I guess how do I know if I'm doing it right from now until I get my iud out? It's going to be sometime next month, due to some issues I've had I need a procedure done to remove it because my gyno cut the strings shorter. I'm sorry if I'm rambling, I feel odd for asking lol.