I'm 17 weeks today, but I started feeling them around 15 weeks. I read that they actually start much earlier, but that women don't generally feel them until later. I spoke with my doc this morning and told him about mine. He said it's totally possible to feel them this early.
Mine most often occur when my bladder is "over full," meaning middle of night or first thing in the morning. I can feel a tightening sensation on the inside and my uterus feels tight to the touch from the outside.
As long as there's no pain, I think you're good.