You can show really early for several reasons. If it's not your first pregnancy you show earlier. Multiples certainly take up more space and show earlier. A cyst or other growth can take up space and make you show earlier. Or if you are a really skinny to begin with you will show earlier. My friend was showing by 8 weeks w/ her second, I swore up and down she had to be having twins but she wasn't, just showing early b/c she was skinny and it was her second.
All the above answers are true. With my first, i didnt show, til like 12 weeks or so, with my second (I lost) I showed a little later than that. With my 3rd(lost at 5 months), I showed about 10-11 weeks and with my twins, i think I showed as soon as I conceived!!! LOL Not really, but it was early on.
Every body is different and people show earlier than some.
Congrats on your pregnancy! :)