21 - No period for 2 months - nothing on ultrasound ..?

If all the pregnancy tests & ultrasounds are still showing nothing, you probably aren't pregnant (although it does happen). The symptoms you listed could be caused by a number of things other than pregnancy, but you would probably feel better if you did get a second opinion (just for your own peace of mind). If you don't get a second opinion & you really think you're pregnant you might always wonder but I really don't think you would be if everything is still showing negative. Good luck & I hope you can conceive :)