Help me late period

So I had a miss carriage October 26 th 2014 After that me and my partner have been using condoms my first period after was on the 25 th november 2014 I was then due on the 22nd December 2014 according to glow and there is still no sign of a period and it's been 7 days I have took a pregnancy test today it was negative I'm never this late and the last time I was this late I fell pregnant without using anything but I've been using condoms.... help???