Can i still be pregnant after passing one clot but hcg level decreased?

so i found out i was pregnant last monday. Super excited bc this would be my 2nd child! 2 days later i started bleeding so i went to the ER (friday june 8 2012) and the docs there said that i was pregnant they didnt see a baby on the ultrasound i wasnt having a tubal and then they did a pelvic exam and the doc said that im not passing any tissue (or thats what it looked like) that i should be fine. well i kept bleeding not heavy i had no cramping or no pain just bleeding but i never soaked a pad then on wednesday jkune 13 2012 i passed a clot about the size of a quarter ( the whole time i was bleeding i never passed a clot or tissue uo until this time) my hcg level read 67.1 at the er then today when i went to the dr they read 51.7. did i miscarry? is it still possible to feel pregnant? cause now im just spotting! still no pain or cramping. need advice and opinions please!