Birth Control

So I'm currently taking Minastrin Fe birth control pills. I've been taking them since December 2013. For the past two months I've missed my period, but in May I had a day of spotting & 3 days of spotting in June. My period for July is not due yet. But after going to my doctor concerned about missing my period she simply instructed me to take a pregnancy test every month if my period does not come. Has this ever happened to any one else or should I just be grateful for not having a period?