Are you a naurally thin person? If you are it may be normal that you haven’t gained too much weight. My best friend was prego. for seven months before she started to show and after she gave birth to her son (who by the way was healthy) she weighed ten punds less that what she weighed before she became prego. But if it really concerns you,you may want to discuss it with your doctor he/she may be able to refer you to see a specialist.