You should visit a doctor as soon as possible, when one is pregnant being in pain shows that there is something wrong. Being a month and a half pregnant pain in your tummy could be anything from bloating to serious infections.
Not trying to scare you but at a month and a half, pain could also be a sign of etopic pregnancy, as well as any above mentioned possibilities. If pains persist, you seriously need to be checked by an OB Doctor
Gotta agree with adam...dr ASAP...there is no room for error when you are expecting...espcially this early in the pregnancy...if there is a problem the dr can take care of it right away...hopefully, all is well and you go on to have a healthy and happy baby...best of luck to you! :-))