If it's been two weeks since you had unprotected sex and the pregnancy test is coming up negative, I would attribute your symptoms to the likelihood that you're about to start your menstrual cycle.
You're probably anxious to know for certain though, so I would wait two more days, and if you still don't have your period, take another test. You can continue testing every 48 hours until you either get a positive test or you begin your menstrual cycle.
The reason to test every 48 hours is that on the slight chance you are pregnant, the pregnancy hormone will double every two days (48 hours).
The reason I think your negative test is probably accurate is that if you had sex two weeks ago, you likely would have experienced implantation within the last two weeks and would have enough hormone by now to get a positive on a pregnancy test. However, since you don't know for certain when (or if) you ovulated there is still a possibility you could be pregnant and it's just too early to get a positive test.
Keep in mind that sore breasts, back pain and abdominal cramps are not uncommon before you start your period.