inconsistent periods

I've never had consistent periods, but have never had trouble getting pregnant. I'm now 27 with two children under two. My husband and I are going to try for a third child come December, but this will be our first planned pregnancy. For the past four months I've been tracking my periods to attempt to get a jump start on gauging my fertility window. Unfortunately, this seems to be pointless. I have not had one period come "on time" or even close. I am currently on "day 44" of my cycle, and have lost all symptoms of a period being near. So my question to you all is, do you have any advice to tracking fertility with an inconsistent period?