What Causes Late Periods After Taking I Pill In Previous Month?

hello,i took ipill on 22 november 2011 and bleeding started on 29 nov.( little spotting daily till 8 dec.) and my actual period date was 12 dec. but then from 8 dec it started bleeding normally as in normal periods days and it continued till 12 dec. i took pregnancy test and blood test too both were negative. but now in january my not came till now....plz help me...wat 2 do...????