sorry read it wrong meant to say you had sex 25th nov,but had a period 8 days before that,so up till dec 6 only 20 days not 12 days that i put,how long are your cycles.you would have been due period 29th 30 right..
so your last period was nov 25th right, so you started to bleed again dec 6th,was this an actual period,it was only 12 days since your nov period.....was it spotting or full flow....you wouldnt have been due period till.22nd dec if your cycle is 28 days that is.im a bit confused if 6 dec was a full period,i would retest few days.
If you had a period 12 days after having sex, I would say you're not pregnant, but from the sounds of the symptoms you're having, it doesn't really make sense. I would do as sck08 said, and if it still comes out neg and you still are having the same issues, call a doc and go from there
Good luck
I would retest in a few days. The spotting could be implantation spotting...