How long until positive pregnancy test?

I had my 2nd child Oct. 15th and got my first and only period on Nov. 27th. It was lighter than usual but lasted about the usual length of time. My husband and I had unprotected sex in my fertile window and about a week later I had light spotting for a couple of days. My period should've arrived Dec. 27th or at least by now and it hasn't. I've been tired, moody and having discharge like my previous pregnancies but all 3 pregnancy tests have been negative. I also have PCOS so I'm wondering if my levels are off again but I honestly haven't had any problems with PCOS since 2010. Any advice?