After having a child and TTC again, I have irregular periods and no idea how long my cycle actually is :/ HELP!

After having my first child in 2013 and getting the nexplanon in my arm in April all I did was bleed for months and months. I got the birth control taken out of my arm in September 2013, 5 months after getting it put in. Since then my periods have been out of whack and it's sometimes impossible to track my period or ovulation for that matter. It's like I don't even know my body anymore. 😞 I don't know what to do!!