I think it is normal to lose weight in the 1st trimeter of pregnancy, make sure your taking your daily folic acid, so your little bean is getting all the vitimans it needs. If you are concerned make an appointment to your docters. As missjen566 says above it might be becasue you have lost your appetite with all the morning sickness, it will eventually go and you will start to get your little bump =) good luck xxx
I'm 6 weeks too! I lost weight too not the same time as u but I did because I had no appetite I wasn't sick or anything just didn't feel like eatin a lot! Don't worry you will gain. Its normal. I'm just now starting to get my appetite back and now I'm worried I'm going to eat too much!! I've been so hungry lately completely opposite of 3 days ago. It changes fast.