What Delayes Menstruation After Removal Of IUD?

hello, my question is, i had my IUD taking out november 9th. and had my first period 4 days after it was taken out. now i'm in december 24 and had no period. i took acouple of pregnancy test to make sure im not pregnant and test came back negative. how long does it take for me to get back on my regular schedule?. or does it mean that im may be pregnant?.