I've heard that nausea and breast tenderness are normal in early pregnancy. If these symptoms aren't there, is that a bad sign?
The sudden surge in hormones can slam a woman's body surprisingly hard. Breast tenderness from increased estrogen, constipation from increased progesterone, and nausea because of the thyroid-like effects of the pregnancy hormone HCG are in fact good signs that the pregnancy is healthy. But we can't rely on these.
Not having these signs is not an omen of doom, however. How things effect a person depends on that person's threshold. Every woman feels pregnancy differently, just as every woman feels labor differently.
If you want to get aggressive (and spend some money that might be wasted), you can get two serial HCG levels 48 hours apart. These values ideally should be about double in early pregnancy. Another test is a serum progesterone level—it should be about 15 or greater. And then there's always the ultrasound, with a good fetal heart rate and size compatible with the gestational age being the final reassurance. Of course if every woman, regardless of risk, had these tests, obstetrical care would become prohibitively expensive. We usually reserve this type of surveillance for women at high risk, for women who are bleeding, and for women with suspicion of ectopic pregnancy in a tube.
When it comes to these symptoms, no news does not mean bad news.