I'm with the others hon, it depends if you are sure of ovulation date. If you ovulated late (say day 20) then that might be OK. My first bt with this pregnancy was 44 but that would have been about 4 weeks 2 days pregnant. It had more than doubled two days later. If you are sure of dates though then that is quite low for 5 weeks. Good luck. I will keep everything crossed that you get good doubling!!!