What Causes Brown Menstrual Flow And Pregnancy Symptoms?

My last day of period was on the 7/10/2010, the month before (sept) i had not been taking my pill regular (mytrogynon 30), however my period was light but seemed normal. When i finished on 07/10/2010 i didnt take my pill again untill the 14 + 15 october and missed every other day inc today.. I am due on the 31st and usually my cycle runs on time but not sure if that is just because of the pill.. However we had unprotected sex quite a few times and i started to feel all the symptoms of a pregnant woman. however i had a little bleed yesterday 26/10 for a couple of hours, then nothing from 4.00pm untill half 6 this morning. I have done two pregnancy tests, one a week a go and one yesterday which were both neg.. I was just wondering as i am getting a little worried.. My flow today is majority of brown and was wondeering if i was pregnant and this was just implant bleeding??