According to the "books" darkening of the aerolas can be a sign. Cramping can happen too.... If you start to spot you may want to test anyway because that is a sign of implantation bleeding.

But you will still have to wait until close to your period for the test to be more accurate...

Good luck, my husband and I were not sucessful this month. But no rush, we just started and I just want to have at least one child before I am 35 and I am only 27.