If this is your first (depending on how far you are) it takes a longer time to feel it. And when you do it's not really consistent. It almost sounds as though it's gas, but I could very well be wrong. It would be my guess anyways.
it sounds like gas but sometimes thats what your baby feels like mine felf more like i had a gold fish flapping around at 1st now it feels like my uterus is stretching
i felt my first movements at 18 weeks with my daughter. it felt like someone had gently poked me with a pen from the inside. and it was very low. i waited a few minutes with my hand in place where i had originally felt it, and sure enough the little booger kicked me again :) if you're guessing on what it is, it probably isn't fetal movement quite yet. you will know for sure when it is! the earliest i have heard of women feeling fetal movement is 16 weeks. but, every woman is different! soon enough it will wake you in your sleep, good luck!