Why Am I Having Period While Positive On Pregnancy Test?

hi there,My last periods on 8 of December 2010 and I am usually 29-30 day cycle, I took Clear blue pregnancy test and result positive 1-2 but then i have my periods on the 9 of January 2011 for 2 and half days and lighter than my normal periods, then i am going to doctor and says was negative. last night i took another clear blue pregnancy test and result positive 3+ can you help me explain whats going on. i am i pregnant?