To me this may sound like an ectopic (sorry to scare you!) i would be getting this followed up with a scan as soon as possible, however if you experiance any pain, ANY PAIN! i would go straight to emergency and get them to run sone test. In fact i would get it checked tonight, but having been there before and not knowing it is scary, i hope for you that it is not the case and that maybe you lost a twin and the other is now growing nicely. It is hard to saw without a medical dix

GL