How old are you? Any other hormonal changes, like birth control, medication, menopause, etc.?

The only times I've ever had really sore boobs was when I was on whacked up birth control.

Boobs can be sore for a number of reasons. They could be sore due to birth control. They could be sore due to an upcoming period. They could just be growing; many womens breasts continue to grow into their 20s. Have you done any workouts lately involving lifting weights or swimming or anything working out the breast area? It could be a side effect from that.

When did you have unprotected sex? If it's been a few weeks, you might want to take a pregnancy test yourself, at home. The sore boobs is a very good indication of pregnancy. Remember, you don't want to take birth control if you are pregnant, so make sure you test soon, if possible.