I just stopped my birth control pill. My last pill was the placebo on Saturday. My period ended on Sunday but today I started having some spotting. Is this withdrawal bleeding?

I was charting as of the first day of my period (today is cd7) but i am wondering if I need to start charting from the end of this possible withdrawal bleeding? I would like to start using opks but this has thrown me and I'm not sure when to start using them....

Any thoughts are appreciated. Also, did you experience any side effects after stopping bcp?