I am not sure why you would have sharp pains in your belly and I have never heard of that being a sign of pregnancy. I would not worry about actually being pregnant until you are five days past your period with no sign of AF (your period).
Also, I would highly recommend you start on birth control if you are having unprotected sex. I cannot tell by this post if you are worried about having a baby or not but if you are not looking for one just "pulling out" will not cut it. There is sperm even in pre-cum and there is no way for him to tell when any has leaked out even if he pulls out way before he actually "goes."
There are many different types of birth control available to girls your age and will keep your information private if you are worried about a bad reaction from your parents. I HIGHLY recommend going to Planned Parenthood, they are great people and will keep you healthy and baby free!