I can't understand what's going on!

I've never missed a period before but I've missed two with in the last few months! I had my last period September 29 and haven't had one sense. I haven't been stressed out more then normal or anything. Within the last few days my boobs have felt strange, I've been peeing more, I've felt super bloated, my back has been killing me, and I've been super moody. I went to the doctor about a month ago to take a blood pregnancy test. Which came back negative. I'm just wondering if I should just go back and see my doctor and see what's going on or should I just not worry about it?