18 days late for period

i am 18 days late for period my last started 24/01/13 , i have taken 6 pregnancy test in the last 10 days al negative apart from one which was a extrmely faint positive , have some symptoms of being pregnant sore boobs, fatigue, nausea , headaches i also have had extreme bloating and sickness at night , me and my fiance have been ttc for around a year nw so hoping i am pregnant would love to give my son a brother or sister , just dont know if i can still be pregnant with so many negative tests...