Spotting is really common with the pill. It is called break thru bleeding and can happen at any time in your cycle. Brown blood is blood that has been sitting around for awhile (old), red blood is fresh.
You can take a pregnancy test with your first morning urine on the first day of your 'missed' period. So whatever day you are starting your placebo pills.
As for all the cravings and the other symptoms you feel you have been experiencing, I don't think they are related to pregnancy. If you have enough pregnancy hormones in your system to cause pregnancy symptoms, you would also have enough hormones in your system to make a pregnancy test POSITIVE (if you were, in fact, pregnant). It is too early for that.
Good luck.