Can start to feel and can .F.E.E.L the baby are two entirely different things. At under 15 weeks the baby is not large enough and the bones are not hardened enough to make a real pushing feel. When the baby gets larger, and there is less room to move in the uterus, is when the most movements can be felt.
I'm not dismissing that you felt the baby move. I just don't think what you felt, that rythmic motion, was the baby. I think it regular ol' sex causing that.
Have no fear though, you'll be having feet up under your ribs and a bladder bouncing baby in no time!
Happy pregnancy to you!