Hello, i was alway petite in size and each of my babies were all over 9lbs when they were born lol. So when i was like 2/3 months pregnant i looked like most people at 5 months. Sometimes it can be also be cause you have lots of amniotic fluid which is a good thing(means your are well hydrated). I would not worry. If you are expecting twins your OBGYN will let you know right away lol. But yes you can show very early sometimes!