B.C.
Every woman and every pregnancy is different.
Unless you had a fertility procedure, it's really hard to pinpoint exactly when conception/implantation took place - so maybe you are not exactly 5 weeks pregnant yet.
At this stage HCG levels can double every 48-72 hours, so the next test should tell you more.
It's hard not to worry, but worrying isn't going to help or change anything - so try to relax and think positive thoughts.
Here is more info about HCG than you probably want to know:
http://www.babymed.com/hcg-level