Could it be wind?? I sometimes get really sharp pains (and not pregnant) when I need to go to the loo really badly and am feeling a bit constipated.
I would think that if you're really worried about it, the only thing that will alleviate your concerns is to see the GP again, are they still open tonight? Even if it's a different doctor, maybe they will have some advice or suggestions. Otherwise make an appointment first thing in the AM if it is still bad. The reality is, that no amount of research of comments from people will totally take away the worry, and only you know how the pain feels. As you already have an appointment booked for friday you could wait until then, if you think you won't stress yourself too much.