I went through the same thing last week. It is important that you know when you ovulated otherwise you are not comparing like with like. A beta of 40 could be good if you ovulated late but low if you ovulated early. It rises very quickly in the first few days, so unless you know when you ovulated (and lets face it high fsh ladies can ovulate anytime!)it is very dangerous to compare. Also, the important thing to bear in mind is that different people get their betas done at different times. My first beta was day 18/19 past O and it came up at 1040, but others get theirs done at day 14 and it would be much lower then.
Hope this helps........those first few days/weeks are agony and nothing can really help you through this until you can see something on ultrasound.