Sore breasts is a classic premenstrual symptom. Trust me!
If these "spots" around her nipples are like pimples, they are perfectly normal and are called montgomery's glands.
While they do tend to enlarge during pregnancy, it's unlikely to be the cause of their appearance this early.
Hcg (human chorionic gonadotrophin) is the chemical that pregnancy tests measure, and is also the chemical that triggers pregnancy symptoms. While some women are particularily sensitive to it's presence, most don't notice any physical changes until the hcg concentration is at least high enough to register on a pregnancy test (most tests detect 100miu of hcg).
There are some tests that detect lower amounts, and one brand is fre (first response early). This test can be used up to four days before her period is due (not with 100% accuracy as implantation times can vary, but with reasonable accuracy). I believe that this tests detects 20miu of hcg.
Give it a try, and if you get a reprieve this time (and I believe you will), please make sure you're well protected in the future.
Good luck.