I too am six weeks and I am experiencing the same thing. My stomach looks like I am 6 months pregnant. My ultra sound is April 5. It is going to drive me crazy because everybody is saying it looks like I am going to have twins. Not sure, but anything is possible. Good Luck.
Congrats.
I found such changes in the starting of my pregnancy. when it was 4 - 6weeks, it appeared as it would appear at 3months..at 7month as if it is 9months pregnancy. there on changes were less but internally growth of the fetus continued.
Looking big doesn't really mean more than one baby. You would get a clear answer after your first ultrasound.
Just like Christine, I got HUGE with my second child and looked almost 6 mths pregnant in less then 3mths due to water retention and was also convinced I was having twins until I got my first ultrasound confirming just one baby. I gained almost the same weight as Christine too at just over 60 lbs and lost most of it within a few mths after having my son. The tenderness in my breasts and how big they got right away was the first sign to me that I was pregnant and is quite common with many women.
I got HUGE with my second child...after barely showing with my first. Oddly enough, my actual weight when I delivered my second wasn't much more than with my first, I just carried it completely differently. I looked 6 months when I was only 3 months...with my first strangers could NOT tell I was even pregnant up to the day I had her!
With first I started at 100lbs/5'6" (yes I was very underweight) and I was about 160 when I had her (mostly water weight, I retained water in my trimester it went away right after I had her and I was 120 within a week of delivery); with second I was about 110lbs at start and 165 when I delivered...was down to about 125 within a week or so.
That was in 1990 and 1992 when I was 20 and 22 respectively.
Certainly anything is possible, but more then likely it's the fact that you are tiny (I have pictures up of my 9 week belly and was pretty big for that time as well) combined with bloating/water retention. Keep in mind that a 6 week baby is smaller then your fingernail at this point, so it is unlikely to be that, even if two. However, nothing is impossible! When do you have your first ultrasound?