am i preagnent

i am on the pill and have been for 5 months now. i had sex on a wednesday 27th early hors of the morning the next day i experienced spotting followed by heavy bleeding then light again for the next 4 days. my period is not due untill the 8th of january, coud this earli period be due to the pill and breakthrough bleeding or could it be implantment bleeding?. i have heard it takes about 4 days for this to occur but could you please settle my nerverd. to add i am on cezatette and took the pilll 4 hours late for three consecutive days. i normay take it at 8 and took it at 12 could this be the reason although you are still pritoected for 12 hours. please help thank you sally