with pregnancy symptoms but had a bleeding

hi, i just want ot ask some questions? i had my period on Dec. 23, 2006 and i was having pregnancy symptoms by the Jan. 11 up to 16th. i was suppose to have myperiod on 19th but on 17th i found out that there are blood clots so small but didnt have my period on that day. That night, the discharge was thred like and still no period. the next day, the 18th, i was now bleeding and my period is due on the 19th. How come this happen? i only use one pad this day and after i changed it, it was like my last day of period. Help!! I'm confused.