missed periods

I haven't had a period since October 30th. I had one a few days after I got off that one that lasted 11 days on September 15th. But since then I haven't had one. I thought I started one the other day and wore a tampon because there was blood in my urine and such. Well when I went to change it there was green discharge and that's all. Nothing since. I took a pregnancy test but it came back negative. I know there are false negatives, should I take another one or go to the doctor?