I Take Birth Control Pills.. And I Missed A Pill

I take birth control pills.. and I missed a pill last month and I missed a pill this month. but I'm supposed to have my period every month on the 11th. and all I had was spotting instead of my period. I'm only 15. I'm freakjng out and don't know what to do. I took a test and it said negative but It could be because I took it so early. any advice on the reason why I missed my period?