Firstly, I do think that what you're describing sounds ALOT like early pg symptoms - the tiredness, weird feelings in your belly, pink spotting (possibly implantation bleeding - where the embryo implants into the uterus) and the nausea etc. Also even though most tests say you can test at any time of the day, it is always best to use your first morning urine, and it is possible to get several negative results before getting a positive, depending on the amount of hormones your body is producing. I would definatley tests again, using the first morning urine and see how you go - if there is no change, definately see your DR, if you aren't pg, such a big change to your cycles could indicate another problem.

And no, you're not in the wrong place