How likely are we to miscarry?

I am about 5 weeks and 4 days and was just reading "Expect Better" which says that 15-20% of women will miscarry within the first 12 weeks. And it says that women that do not feel nausea within the first trimester are more likely to miscarry. I'm freaking out because I haven't felt nausea at all. My first appointment isn't for another 2 weeks. Is there a way to check my HCG levels before then? To the women who miscarried before - were there any signs that it was coming beforehand? I would appreciate all the advice I can get. Thank you guys so much for your help and support! Not sure what I'd do without this amazing community!