Is Pregnancy Possible Through Withdrawal Method Of Intercourse?

Could I possibly be pregnant? My boyfriend and I use to pull out method and I ve recently read about how ineffective that can be. I m mainly worried that I could be pregnant because.. I was ovulating March 10-16 On March 17 I had noticed very slight bleeding when I was cleaning in the shower and that was it for that day. Since then it has been 1 week and I had very light spotting again yesterday. This has NEVER happened to me before. I read online that you can spot during pregnancy but i haven t found anything or anyone with the same situation. I m due to start my period March 29th. Does the timing of everything sound like I could be spotting from pregnancy or implantation bleeding?? Have you spotting during pregnancy? Have you had a similar situation? Please help(: thank you